Default UseAccessLevelOnImports to false (#2047)

## Motivation

After the discussion on
#2042 (comment), I
played a bit more with `InternalImportsByDefault` and the different
generator options, got to the following conclusions:

- If you add `import Foo` to some file, where `Foo` is also being
imported with an explicit `internal` access-level modifier _in the
generated code_, it will work as long as `InternalImportsByDefault` is
enabled.
- If you disable `InternalImportsByDefault` for the corresponding target
in `Package.swift`, you get an `"Ambiguous implicit access level for
import of 'Foo'; it is imported as 'internal' elsewhere"` **error** (not
a warning). This means that if the code generator plugin(s) begin adding
the access level modifiers by default based on how they're built, they
could cause source-breakages for users unintentionally.
- _This isn't any different between language mode 5 or 6_ - I tried
changing the target's language mode and the behaviour is the same as
described above in either case.

Given all this, defaulting `UseAccessLevelOnImports` to `false`
**always** for now may be the easiest (and least surprising, from a
users' perspective) thing to do, until `InternalImportsByDefault` are
enabled by default in a future Swift >6.0 version (as the proposal
states), where we can default to `true` again:
```
#if compiler(>=6.x) // where x is the version where internal imports by default is enabled
// default to true
#else
// default to false
#endif
```

The rationale behind this is that adding access levels to imports on
your code is currently totally optional. If you choose to start adding
them explicitly, then it's okay to also have to tell your
tooling/generators that they should also add them explicitly. If you
don't, they'll keep generating things the exact same way they've been
doing it, which is what users of the generator would expect.

## Modifications
- Default `UseAccessLevelOnImports` to `false` always.
- Regenerate protos
- Remove `InternalImportsByDefault` from test and executable targets,
since it doesn't make a lot of sense to have access level modifiers on
imports here anyways as these targets cannot be imported.

Author: gjcairo

Examples/v2/echo/Generated/echo.grpc.swift

@@ -21,8 +21,8 @@
 // For information on using the generated types, please see the documentation:
 //   https://github.com/grpc/grpc-swift
 
-internal import GRPCCore
-internal import GRPCProtobuf
+import GRPCCore
+import GRPCProtobuf
 
 internal enum Echo_Echo {
     internal static let descriptor = GRPCCore.ServiceDescriptor.echo_Echo

Examples/v2/echo/Subcommands/Collect.swift

@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-internal import ArgumentParser
-private import GRPCCore
-private import GRPCHTTP2Core
-private import GRPCHTTP2TransportNIOPosix
+import ArgumentParser
+import GRPCCore
+import GRPCHTTP2Core
+import GRPCHTTP2TransportNIOPosix
 
 @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
 struct Collect: AsyncParsableCommand {

Examples/v2/hello-world/Generated/helloworld.grpc.swift

@@ -21,8 +21,8 @@
 // For information on using the generated types, please see the documentation:
 //   https://github.com/grpc/grpc-swift
 
-internal import GRPCCore
-internal import GRPCProtobuf
+import GRPCCore
+import GRPCProtobuf
 
 internal enum Helloworld_Greeter {
     internal static let descriptor = GRPCCore.ServiceDescriptor.helloworld_Greeter

Examples/v2/hello-world/HelloWorld.swift

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-internal import ArgumentParser
+import ArgumentParser
 
 @main
 @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)

Examples/v2/hello-world/Subcommands/Greet.swift

@@ -14,9 +14,9 @@
  * limitations under the License.
  */
 
-internal import ArgumentParser
-internal import GRPCHTTP2Transport
-internal import GRPCProtobuf
+import ArgumentParser
+import GRPCHTTP2Transport
+import GRPCProtobuf
 
 @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
 struct Greet: AsyncParsableCommand {

Examples/v2/hello-world/Subcommands/Serve.swift

@@ -14,9 +14,9 @@
  * limitations under the License.
  */
 
-internal import ArgumentParser
-internal import GRPCHTTP2Transport
-internal import GRPCProtobuf
+import ArgumentParser
+import GRPCHTTP2Transport
+import GRPCProtobuf
 
 @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
 struct Serve: AsyncParsableCommand {

Examples/v2/route-guide/Generated/route_guide.grpc.swift

@@ -21,8 +21,8 @@
 // For information on using the generated types, please see the documentation:
 //   https://github.com/grpc/grpc-swift
 
-internal import GRPCCore
-internal import GRPCProtobuf
+import GRPCCore
+import GRPCProtobuf
 
 internal enum Routeguide_RouteGuide {
     internal static let descriptor = GRPCCore.ServiceDescriptor.routeguide_RouteGuide

Package@swift-6.swift

@@ -346,8 +346,7 @@ extension Target {
       ],
       swiftSettings: [
         .swiftLanguageMode(.v6),
-        .enableUpcomingFeature("ExistentialAny"),
-        .enableUpcomingFeature("InternalImportsByDefault")
+        .enableUpcomingFeature("ExistentialAny")
       ]
     )
   }
@@ -710,8 +709,7 @@ extension Target {
       path: "Examples/v2/echo",
       swiftSettings: [
         .swiftLanguageMode(.v6),
-        .enableUpcomingFeature("ExistentialAny"),
-        .enableUpcomingFeature("InternalImportsByDefault")
+        .enableUpcomingFeature("ExistentialAny")
       ]
     )
   }
@@ -773,8 +771,7 @@ extension Target {
       ],
       swiftSettings: [
         .swiftLanguageMode(.v6),
-        .enableUpcomingFeature("ExistentialAny"),
-        .enableUpcomingFeature("InternalImportsByDefault")
+        .enableUpcomingFeature("ExistentialAny")
       ]
     )
   }
@@ -837,8 +834,7 @@ extension Target {
       ],
       swiftSettings: [
         .swiftLanguageMode(.v6),
-        .enableUpcomingFeature("ExistentialAny"),
-        .enableUpcomingFeature("InternalImportsByDefault")
+        .enableUpcomingFeature("ExistentialAny")
       ]
     )
   }

Sources/GRPCCore/Documentation.docc/Tutorials/Route-Guide/Resources/route-guide-sec03-step04-gen-grpc.txt

@@ -2,5 +2,4 @@ $ protoc --plugin=.build/debug/protoc-gen-grpc-swift \
   -I Protos \
   --grpc-swift_out=Sources/Generated \
   --grpc-swift_opt=_V2=true \
-  --grpc-swift_opt=UseAccessLevelOnImports=false \
   Protos/route_guide.proto

Sources/performance-worker/BenchmarkClient.swift

@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-private import Foundation
-internal import GRPCCore
-private import NIOConcurrencyHelpers
-private import Synchronization
+import Foundation
+import GRPCCore
+import NIOConcurrencyHelpers
+import Synchronization
 
 @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
 final class BenchmarkClient: Sendable {