add missing imports

Author: rnro

Sources/GRPCCodeGen/CodeGenerationRequest.swift

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+import Foundation
+
 /// Describes the services, dependencies and trivia from an IDL file,
 /// and the IDL itself through its specific serializer and deserializer.
 public struct CodeGenerationRequest {

Sources/GRPCCodeGen/Internal/Translator/Docs.swift

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+import Foundation
+
 package enum Docs {
   package static func suffix(_ header: String, withDocs footer: String) -> String {
     if footer.isEmpty {

Tests/GRPCCoreTests/Configuration/ServiceConfigCodingTests.swift

@@ -16,6 +16,7 @@
 
 import Foundation
 import GRPCCore
+import SwiftProtobuf
 import XCTest
 
 final class ServiceConfigCodingTests: XCTestCase {

Tests/GRPCCoreTests/Test Utilities/Services/HelloWorld.swift

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+import Foundation
 import GRPCCore
 
 struct HelloWorld: RegistrableRPCService {