Implements verifier and code gen for swift (#6373)

Updates test cases on linux

Adhere to new protocol naming

Adds fuzzing

Adds documentation

Adds support for string unions

Updated fuzzer generated code

swift/Sources/FlatBuffers/Root.swift

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2021 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import Foundation
+
+/// Takes in a prefixed sized buffer, where the prefixed size would be skipped.
+/// And would verify that the buffer passed is a valid `Flatbuffers` Object.
+/// - Parameters:
+///   - byteBuffer: Buffer that needs to be checked and read
+///   - options: Verifier options
+/// - Throws: FlatbuffersErrors
+/// - Returns: Returns a valid, checked Flatbuffers object
+public func getPrefixedSizeCheckedRoot<T: FlatBufferObject & Verifiable>(
+  byteBuffer: inout ByteBuffer,
+  options: VerifierOptions = .init()) throws -> T
+{
+  byteBuffer.skipPrefix()
+  return try getCheckedRoot(byteBuffer: &byteBuffer, options: options)
+}
+
+/// Takes in a prefixed sized buffer, where the prefixed size would be skipped.
+/// Returns a `NON-Checked` flatbuffers object
+/// - Parameter byteBuffer: Buffer that contains data
+/// - Returns: Returns a Flatbuffers object
+public func getPrefixedSizeRoot<T: FlatBufferObject>(byteBuffer: inout ByteBuffer) -> T {
+  byteBuffer.skipPrefix()
+  return getRoot(byteBuffer: &byteBuffer)
+
+}
+
+/// Verifies that the buffer passed is a valid `Flatbuffers` Object.
+/// - Parameters:
+///   - byteBuffer: Buffer that needs to be checked and read
+///   - options: Verifier options
+/// - Throws: FlatbuffersErrors
+/// - Returns: Returns a valid, checked Flatbuffers object
+public func getCheckedRoot<T: FlatBufferObject & Verifiable>(
+  byteBuffer: inout ByteBuffer,
+  options: VerifierOptions = .init()) throws -> T
+{
+  var verifier = try Verifier(buffer: &byteBuffer, options: options)
+  try ForwardOffset<T>.verify(&verifier, at: 0, of: T.self)
+  return T.init(
+    byteBuffer,
+    o: Int32(byteBuffer.read(def: UOffset.self, position: byteBuffer.reader)) + Int32(byteBuffer.reader))
+}
+
+/// Returns a `NON-Checked` flatbuffers object
+/// - Parameter byteBuffer: Buffer that contains data
+/// - Returns: Returns a Flatbuffers object
+public func getRoot<T: FlatBufferObject>(byteBuffer: inout ByteBuffer) -> T {
+  T.init(
+    byteBuffer,
+    o: Int32(byteBuffer.read(def: UOffset.self, position: byteBuffer.reader)) + Int32(byteBuffer.reader))
+}