Return this in Map#set and Set#add (#1104)

Author: MaxGraey

std/assembly/index.d.ts

@@ -1535,7 +1535,7 @@ interface RegExp {}
 declare class Map<K,V> {
   readonly size: i32;
   has(key: K): bool;
-  set(key: K, value: V): void;
+  set(key: K, value: V): this;
   get(key: K): V;
   delete(key: K): bool;
   clear(): void;
@@ -1547,7 +1547,7 @@ declare class Map<K,V> {
 declare class Set<K> {
   readonly size: i32;
   has(value: K): bool;
-  add(value: K): void;
+  add(value: K): this;
   delete(value: K): bool;
   clear(): void;
   values(): K[]; // preliminary

std/assembly/map.ts

@@ -113,7 +113,7 @@ export class Map<K,V> {
   }
 
   @operator("[]=")
-  set(key: K, value: V): void {
+  set(key: K, value: V): this {
     var hashCode = HASH<K>(key);
     var entry = this.find(key, hashCode); // unmanaged!
     if (entry) {
@@ -151,6 +151,7 @@ export class Map<K,V> {
       entry.taggedNext = load<usize>(bucketPtrBase);
       store<usize>(bucketPtrBase, changetype<usize>(entry));
     }
+    return this;
   }
 
   delete(key: K): bool {

std/assembly/set.ts

@@ -101,7 +101,7 @@ export class Set<T> {
     return this.find(key, HASH<T>(key)) !== null;
   }
 
-  add(key: T): void {
+  add(key: T): this {
     var hashCode = HASH<T>(key);
     var entry = this.find(key, hashCode); // unmanaged!
     if (!entry) {
@@ -124,6 +124,7 @@ export class Set<T> {
       entry.taggedNext = load<usize>(bucketPtrBase);
       store<usize>(bucketPtrBase, changetype<usize>(entry));
     }
+    return this;
   }
 
   @operator("[]=")