Enable MemberImportVisibility check on all targets (#16)

Enable MemberImportVisibility check on all targets. Use a standard
string header and footer to bracket the new block for ease of updating
in the future with scripts.

---------

Co-authored-by: George Barnett <[email protected]>

Author: rnro

Package.swift

@@ -55,6 +55,7 @@ let defaultSwiftSettings: [SwiftSetting] = [
   .swiftLanguageMode(.v6),
   .enableUpcomingFeature("ExistentialAny"),
   .enableUpcomingFeature("InternalImportsByDefault"),
+  .enableUpcomingFeature("MemberImportVisibility"),
 ]
 
 let targets: [Target] = [

Sources/GRPCInteropTests/InteroperabilityTestCases.swift

@@ -15,6 +15,7 @@
  */
 
 internal import GRPCCore
+private import SwiftProtobuf
 
 private import struct Foundation.Data
 

Sources/GRPCInteropTests/TestService.swift

@@ -16,6 +16,7 @@
 
 private import Foundation
 public import GRPCCore
+private import SwiftProtobuf
 
 public struct TestService: Grpc_Testing_TestService.ServiceProtocol {
   public init() {}

Tests/GRPCHealthServiceTests/HealthTests.swift

@@ -17,6 +17,7 @@
 import GRPCCore
 import GRPCHealthService
 import GRPCInProcessTransport
+import SwiftProtobuf
 import XCTest
 
 final class HealthTests: XCTestCase {