[Swift] Flexbuffers native swift port (#8577)

* Offical Swift port for FlexBuffers

This is the offical port for FlexBuffers within
swift, and it introcudes a Common Module where code
is shared between flatbuffers and flexbuffers.

Writing most supported values like maps, vectors,
nil and scalars into a flexbuffer buffer. And includes
tests to verify that its similar to cpp

* Reading a flexbuffer

Implementing reading from a flexbuffer, enabling
most of the buffers features, like most types, maps, vectors,
typedvectors, and fixedtypedvectors.

Currently, if an offset/object cant be read we default to a swift
nil instead of the default flexbuffers 'null' with all values.

* Fixes bazel breaking due to new project structure

Address warnings within the library

* Adds comment on why we added the code & properly enforce the amout of bytes needed

swift/Sources/Common/Int+extension.swift

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2024 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
+
+extension Int {
+
+  /// Moves the current int into the nearest power of two
+  ///
+  /// This is used since the UnsafeMutableRawPointer will face issues when writing/reading
+  /// if the buffer alignment exceeds that actual size of the buffer
+  @inline(__always)
+  public var convertToPowerofTwo: Int {
+    guard self > 0 else { return 1 }
+    var n = UInt32(self)
+
+    #if arch(arm) || arch(i386)
+    let max = UInt32(Int.max)
+    #else
+    let max = UInt32.max
+    #endif
+
+    n -= 1
+    n |= n >> 1
+    n |= n >> 2
+    n |= n >> 4
+    n |= n >> 8
+    n |= n >> 16
+    if n != max {
+      n += 1
+    }
+
+    return Int(n)
+  }
+}