This is the last of the big changes to the js code

This Pr largely tightens up a lot of the code. 'v8' is no longer imported
outside of js. A number of helper functions have been moved to the js.Context.
For example, js.Function.getName used to call:

```zig
return js.valueToString(allocator, name, self.context.isolate, self.context.v8_context);
```

It now calls:

```zig
return self.context.valueToString(name, .{ .allocator = allocator });
```

Page.main_context has been renamed to `Page.js`. This, in combination with new
promise helpers, turns:

```zig
const resolver = page.main_context.createPromiseResolver();
try resolver.resolve({});
return resolver.promise();
```

into:

```zig
return page.js.resolvePromise({});
```

Author: karlseguin

src/browser/ScriptManager.zig

@@ -663,7 +663,7 @@ const Script = struct {
             .cacheable = cacheable,
         });
 
-        const js_context = page.main_context;
+        const js_context = page.js;
         var try_catch: js.TryCatch = undefined;
         try_catch.init(js_context);
         defer try_catch.deinit();
@@ -707,10 +707,10 @@ const Script = struct {
         switch (callback) {
             .string => |str| {
                 var try_catch: js.TryCatch = undefined;
-                try_catch.init(page.main_context);
+                try_catch.init(page.js);
                 defer try_catch.deinit();
 
-                _ = page.main_context.exec(str, typ) catch |err| {
+                _ = page.js.exec(str, typ) catch |err| {
                     const msg = try_catch.err(page.arena) catch @errorName(err) orelse "unknown";
                     log.warn(.user_script, "script callback", .{
                         .url = self.url,

src/browser/cssom/CSSStyleSheet.zig

@@ -79,9 +79,7 @@ pub fn _replace(self: *CSSStyleSheet, text: []const u8, page: *Page) !js.Promise
     // TODO: clear self.css_rules
     // parse text and re-populate self.css_rules
 
-    const resolver = page.main_context.createPromiseResolver();
-    try resolver.resolve({});
-    return resolver.promise();
+    return page.js.resolvePromise({});
 }
 
 pub fn _replaceSync(self: *CSSStyleSheet, text: []const u8) !void {

src/browser/dom/Animation.zig

@@ -49,7 +49,7 @@ pub fn get_pending(self: *const Animation) bool {
 
 pub fn get_finished(self: *Animation, page: *Page) !js.Promise {
     if (self.finished_resolver == null) {
-        const resolver = page.main_context.createPromiseResolver();
+        const resolver = page.js.createPromiseResolver(.none);
         try resolver.resolve(self);
         self.finished_resolver = resolver;
     }
@@ -59,7 +59,7 @@ pub fn get_finished(self: *Animation, page: *Page) !js.Promise {
 pub fn get_ready(self: *Animation, page: *Page) !js.Promise {
     // never resolved, because we're always "finished"
     if (self.ready_resolver == null) {
-        const resolver = page.main_context.createPromiseResolver();
+        const resolver = page.js.createPromiseResolver(.none);
         self.ready_resolver = resolver;
     }
     return self.ready_resolver.?.promise();

src/browser/dom/document.zig

@@ -304,7 +304,7 @@ pub const Document = struct {
             return obj;
         }
 
-        const obj = try page.main_context.newArray(0).persist();
+        const obj = try page.js.createArray(0).persist();
         state.adopted_style_sheets = obj;
         return obj;
     }

src/browser/dom/shadow_root.zig

@@ -50,7 +50,7 @@ pub const ShadowRoot = struct {
             return obj;
         }
 
-        const obj = try page.main_context.newArray(0).persist();
+        const obj = try page.js.createArray(0).persist();
         self.adopted_style_sheets = obj;
         return obj;
     }

src/browser/fetch/Headers.zig

@@ -24,7 +24,6 @@ const Page = @import("../page.zig").Page;
 
 const iterator = @import("../iterator/iterator.zig");
 
-const v8 = @import("v8");
 // https://developer.mozilla.org/en-US/docs/Web/API/Headers
 const Headers = @This();
 

src/browser/fetch/Request.zig

@@ -27,8 +27,6 @@ const Response = @import("./Response.zig");
 const Http = @import("../../http/Http.zig");
 const ReadableStream = @import("../streams/ReadableStream.zig");
 
-const v8 = @import("v8");
-
 const Headers = @import("Headers.zig");
 const HeadersInit = @import("Headers.zig").HeadersInit;
 
@@ -245,20 +243,15 @@ pub fn _bytes(self: *Response, page: *Page) !js.Promise {
     if (self.body_used) {
         return error.TypeError;
     }
-
-    const resolver = page.main_context.createPromiseResolver();
-
-    try resolver.resolve(self.body);
     self.body_used = true;
-    return resolver.promise();
+    return page.js.resolvePromise(self.body);
 }
 
 pub fn _json(self: *Response, page: *Page) !js.Promise {
     if (self.body_used) {
         return error.TypeError;
     }
-
-    const resolver = page.main_context.createPromiseResolver();
+    self.body_used = true;
 
     if (self.body) |body| {
         const p = std.json.parseFromSliceLeaky(
@@ -271,25 +264,17 @@ pub fn _json(self: *Response, page: *Page) !js.Promise {
             return error.SyntaxError;
         };
 
-        try resolver.resolve(p);
-    } else {
-        try resolver.resolve(null);
+        return page.js.resolvePromise(p);
     }
-
-    self.body_used = true;
-    return resolver.promise();
+    return page.js.resolvePromise(null);
 }
 
 pub fn _text(self: *Response, page: *Page) !js.Promise {
     if (self.body_used) {
         return error.TypeError;
     }
-
-    const resolver = page.main_context.createPromiseResolver();
-
-    try resolver.resolve(self.body);
     self.body_used = true;
-    return resolver.promise();
+    return page.js.resolvePromise(self.body);
 }
 
 const testing = @import("../../testing.zig");

src/browser/fetch/Response.zig

@@ -20,8 +20,6 @@ const std = @import("std");
 const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 
-const v8 = @import("v8");
-
 const HttpClient = @import("../../http/Client.zig");
 const Http = @import("../../http/Http.zig");
 const URL = @import("../../url.zig").URL;
@@ -170,24 +168,17 @@ pub fn _bytes(self: *Response, page: *Page) !js.Promise {
         return error.TypeError;
     }
 
-    const resolver = js.PromiseResolver{
-        .context = page.main_context,
-        .resolver = v8.PromiseResolver.init(page.main_context.v8_context),
-    };
-
-    try resolver.resolve(self.body);
     self.body_used = true;
-    return resolver.promise();
+    return page.js.resolvePromise(self.body);
 }
 
 pub fn _json(self: *Response, page: *Page) !js.Promise {
     if (self.body_used) {
         return error.TypeError;
     }
 
-    const resolver = page.main_context.createPromiseResolver();
-
     if (self.body) |body| {
+        self.body_used = true;
         const p = std.json.parseFromSliceLeaky(
             std.json.Value,
             page.call_arena,
@@ -198,25 +189,18 @@ pub fn _json(self: *Response, page: *Page) !js.Promise {
             return error.SyntaxError;
         };
 
-        try resolver.resolve(p);
-    } else {
-        try resolver.resolve(null);
+        return page.js.resolvePromise(p);
     }
-
-    self.body_used = true;
-    return resolver.promise();
+    return page.js.resolvePromise(null);
 }
 
 pub fn _text(self: *Response, page: *Page) !js.Promise {
     if (self.body_used) {
         return error.TypeError;
     }
-
-    const resolver = page.main_context.createPromiseResolver();
-
-    try resolver.resolve(self.body);
     self.body_used = true;
-    return resolver.promise();
+
+    return page.js.resolvePromise(self.body);
 }
 
 const testing = @import("../../testing.zig");

src/browser/fetch/fetch.zig

@@ -131,7 +131,7 @@ pub fn fetch(input: RequestInput, options: ?RequestInit, page: *Page) !js.Promis
 
     try page.requestCookie(.{}).headersForRequest(arena, req.url, &headers);
 
-    const resolver = try page.main_context.createPersistentPromiseResolver(.page);
+    const resolver = try page.js.createPromiseResolver(.page);
 
     const fetch_ctx = try arena.create(FetchContext);
     fetch_ctx.* = .{

src/browser/html/AbortController.zig

@@ -118,7 +118,7 @@ pub const AbortSignal = struct {
     };
     pub fn _throwIfAborted(self: *const AbortSignal, page: *Page) ThrowIfAborted {
         if (self.aborted) {
-            const ex = page.main_context.throw(self.reason orelse DEFAULT_REASON);
+            const ex = page.js.throw(self.reason orelse DEFAULT_REASON);
             return .{ .exception = ex };
         }
         return .{ .undefined = {} };