[Swift] Optional Scalars Preparation (#6028)

* Perpares swift to take optional scalars + adds optional string helper method + disables linters in generated code

* Small fix for generated code

* Update grpc support to alpha 17 for swift

tests/FlatBuffers.GRPC.Swift/Package.swift

@@ -12,7 +12,7 @@ let package = Package(
     dependencies: [
         // Main SwiftNIO package
         .package(path: "../../swift"),
-        .package(url: "https://github.com/grpc/grpc-swift.git", from: "1.0.0-alpha.9")
+        .package(url: "https://github.com/grpc/grpc-swift.git", from: "1.0.0-alpha.17")
     ],
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.

tests/FlatBuffers.GRPC.Swift/Sources/Model/greeter.grpc.swift

@@ -53,13 +53,13 @@ public extension GreeterProvider {
 	func handleMethod(_ methodName: String, callHandlerContext: CallHandlerContext) -> GRPCCallHandler? {
 		switch methodName {
 		case "SayHello":
-		return UnaryCallHandler(callHandlerContext: callHandlerContext) { context in
+		return CallHandlerFactory.makeUnary(callHandlerContext: callHandlerContext) { context in
 			return { request in
 				self.SayHello(request, context: context)
 			}
 		}
 		case "SayManyHellos":
-		return ServerStreamingCallHandler(callHandlerContext: callHandlerContext) { context in
+		return CallHandlerFactory.makeServerStreaming(callHandlerContext: callHandlerContext) { context in
 			return { request in
 				self.SayManyHellos(request: request, context: context)
 			}

tests/FlatBuffers.GRPC.Swift/Sources/Model/greeter_generated.swift

@@ -1,4 +1,5 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+// swiftlint:disable all
 
 import FlatBuffers