[Swift] Implements FlatbuffersVector which confirms to RandomAccessCollection (#8752)

* Implements FlatbuffersVector in swift

Implements FlatbuffersVector which confirms to RandomAccessCollection,
this would give us semi-native sugary syntax to all the arrays in swift port.

This work will also be the foundation of using arrays in swift

* Fix failing tests for Swift

grpc/examples/swift/Greeter/Sources/server/main.swift

@@ -32,8 +32,7 @@ class Greeter: models_GreeterProvider {
 
   func SayHello(
     request: Message<models_HelloRequest>,
-    context: StatusOnlyCallContext
-  )
+    context: StatusOnlyCallContext)
     -> EventLoopFuture<Message<models_HelloReply>>
   {
     let recipient = request.object.name ?? "Stranger"
@@ -48,15 +47,14 @@ class Greeter: models_GreeterProvider {
 
   func SayManyHellos(
     request: Message<models_HelloRequest>,
-    context: StreamingResponseCallContext<Message<models_HelloReply>>
-  )
+    context: StreamingResponseCallContext<Message<models_HelloReply>>)
     -> EventLoopFuture<GRPCStatus>
   {
     for name in greetings {
       var builder = FlatBufferBuilder()
       let off =
         builder
-        .create(string: "\(name) \(request.object.name ?? "Unknown")")
+          .create(string: "\(name) \(request.object.name ?? "Unknown")")
       let root = models_HelloReply.createHelloReply(
         &builder,
         messageOffset: off)