Remove '@_exported import GRPCCore' (#2109)

Motivation:

We added '@_exported import GRPCCore' to transport modules to make it
easier for users as it saves them from adding an import. On reflection
we've our position on this has changed and the implicit dependency will
likely make things less clear.

Modifications:

- Remove exported import from in-proc transport
- Update tutorials/examples to have explicit 'GRPCCore' imports

Result:

More explicit dependencies

Author: glbrntt

Examples/echo/Package.swift

@@ -21,6 +21,7 @@ let package = Package(
   name: "echo",
   platforms: [.macOS("15.0")],
   dependencies: [
+    .package(url: "https://github.com/grpc/grpc-swift", exact: "2.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-protobuf", exact: "1.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-nio-transport", branch: "1.0.0-alpha.1"),
     .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
@@ -29,6 +30,7 @@ let package = Package(
     .executableTarget(
       name: "echo",
       dependencies: [
+        .product(name: "GRPCCore", package: "grpc-swift"),
         .product(name: "GRPCNIOTransportHTTP2", package: "grpc-swift-nio-transport"),
         .product(name: "GRPCProtobuf", package: "grpc-swift-protobuf"),
         .product(name: "ArgumentParser", package: "swift-argument-parser"),

Examples/hello-world/Package.swift

@@ -21,6 +21,7 @@ let package = Package(
   name: "hello-world",
   platforms: [.macOS("15.0")],
   dependencies: [
+    .package(url: "https://github.com/grpc/grpc-swift", exact: "2.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-protobuf", exact: "1.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-nio-transport", exact: "1.0.0-alpha.1"),
     .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
@@ -29,6 +30,7 @@ let package = Package(
     .executableTarget(
       name: "hello-world",
       dependencies: [
+        .product(name: "GRPCCore", package: "grpc-swift"),
         .product(name: "GRPCNIOTransportHTTP2", package: "grpc-swift-nio-transport"),
         .product(name: "GRPCProtobuf", package: "grpc-swift-protobuf"),
         .product(name: "ArgumentParser", package: "swift-argument-parser"),

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

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 import GRPCProtobuf
 

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

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 import GRPCProtobuf
 

Examples/route-guide/Package.swift

@@ -21,6 +21,7 @@ let package = Package(
   name: "route-guide",
   platforms: [.macOS("15.0")],
   dependencies: [
+    .package(url: "https://github.com/grpc/grpc-swift", exact: "2.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-protobuf", exact: "1.0.0-alpha.1"),
     .package(url: "https://github.com/grpc/grpc-swift-nio-transport", exact: "1.0.0-alpha.1"),
     .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
@@ -29,6 +30,7 @@ let package = Package(
     .executableTarget(
       name: "route-guide",
       dependencies: [
+        .product(name: "GRPCCore", package: "grpc-swift"),
         .product(name: "GRPCNIOTransportHTTP2", package: "grpc-swift-nio-transport"),
         .product(name: "GRPCProtobuf", package: "grpc-swift-protobuf"),
         .product(name: "ArgumentParser", package: "swift-argument-parser"),

Examples/route-guide/Sources/Subcommands/GetFeature.swift

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 
 struct GetFeature: AsyncParsableCommand {

Examples/route-guide/Sources/Subcommands/ListFeatures.swift

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 
 struct ListFeatures: AsyncParsableCommand {

Examples/route-guide/Sources/Subcommands/RecordRoute.swift

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 
 struct RecordRoute: AsyncParsableCommand {

Examples/route-guide/Sources/Subcommands/RouteChat.swift

@@ -15,6 +15,7 @@
  */
 
 import ArgumentParser
+import GRPCCore
 import GRPCNIOTransportHTTP2
 
 struct RouteChat: AsyncParsableCommand {

Examples/route-guide/Sources/Subcommands/Serve.swift

@@ -16,6 +16,7 @@
 
 import ArgumentParser
 import Foundation
+import GRPCCore
 import GRPCNIOTransportHTTP2
 import GRPCProtobuf
 import Synchronization