[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/FlexBuffers/Utils/functions.swift

@@ -0,0 +1,158 @@
+/*
+ * 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
+
+@inline(__always)
+internal func isInline(_ t: FlexBufferType) -> Bool {
+  return t <= .float || t == .bool
+}
+
+@inline(__always)
+private func check(_ v: UInt64, width: UInt64) -> Bool {
+  (v & ~((.one << width) &- 1)) == 0
+}
+
+@inline(__always)
+internal func widthI(_ v: Int64) -> BitWidth {
+  let u = UInt64(bitPattern: v) << 1
+  return widthU(v >= 0 ? u : ~u)
+}
+
+@inline(__always)
+internal func widthF(_ v: Double) -> BitWidth {
+  Double(Float(v)) == v ? .w32 : .w64
+}
+
+@inline(__always)
+internal func widthU(_ v: UInt64) -> BitWidth {
+  if check(v, width: 8) { return .w8 }
+  if check(v, width: 16) { return .w16 }
+  if check(v, width: 32) { return .w32 }
+  return .w64
+}
+
+@inline(__always)
+internal func packedType(bitWidth: BitWidth, type: FlexBufferType) -> UInt8 {
+  numericCast(bitWidth.rawValue | (type.rawValue << 2))
+}
+
+@inline(__always)
+func getScalarType<T>(type: T.Type) -> FlexBufferType where T: Scalar {
+  if T.self is (any BinaryFloatingPoint.Type) {
+    return .float
+  }
+
+  if T.self is Bool.Type {
+    return .bool
+  }
+
+  if T.self is (any UnsignedInteger.Type) {
+    return .uint
+  }
+
+  return .int
+}
+
+@inline(__always)
+func toTypedVector(type: FlexBufferType, length: UInt64) -> FlexBufferType {
+  let type: UInt64 = switch length {
+  case 0: type.rawValue &- FlexBufferType.int.rawValue &+ FlexBufferType
+    .vectorInt.rawValue
+  case 2: type.rawValue &- FlexBufferType.int.rawValue &+ FlexBufferType
+    .vectorInt2.rawValue
+  case 3: type.rawValue &- FlexBufferType.int.rawValue &+ FlexBufferType
+    .vectorInt3.rawValue
+  case 4: type.rawValue &- FlexBufferType.int.rawValue &+ FlexBufferType
+    .vectorInt4.rawValue
+  default: 0
+  }
+  return FlexBufferType(rawValue: type) ?? .null
+}
+
+@inline(__always)
+func isTypedVectorElementType(type: FlexBufferType) -> Bool {
+  return type >= .int && type <= .string || type == .bool
+}
+
+@inline(__always)
+func isTypedVectorType(type: FlexBufferType) -> Bool {
+  return type >= .vectorInt && type <= .vectorString || type == .vectorBool
+}
+
+@inline(__always)
+func toTypedVectorElementType(type: FlexBufferType) -> FlexBufferType? {
+  return FlexBufferType(
+    rawValue: type.rawValue &- FlexBufferType.vectorInt
+      .rawValue &+ FlexBufferType.int.rawValue)
+}
+
+@inline(__always)
+func isFixedTypedVectorType(type: FlexBufferType) -> Bool {
+  return type >= .vectorInt2 && type <= .vectorFloat4
+}
+
+@inline(__always)
+func toFixedTypedVectorElementType(type: FlexBufferType)
+  -> (type: FlexBufferType?, count: Int)
+{
+  assert(isFixedTypedVectorType(type: type))
+  let fixedType: UInt64 = numericCast(
+    type.rawValue &- FlexBufferType.vectorInt2
+      .rawValue)
+  let len: Int = numericCast((fixedType / 3) + 2)
+  return (
+    FlexBufferType(rawValue: (fixedType % 3) + FlexBufferType.int.rawValue),
+    len)
+}
+
+// MARK: - Reader functions
+
+@inline(__always)
+func binarySearch(
+  vector: TypedVector,
+  target: String) -> Int?
+{
+  var left = 0
+  var right = vector.count
+
+  while left <= right {
+    let mid = left &+ (right &- left) / 2
+    let comp = vector.compare(offset: mid, target: target)
+    if comp == 0 {
+      return mid
+    } else if comp < 0 {
+      left = mid &+ 1
+    } else {
+      right = mid &- 1
+    }
+  }
+  return nil
+}
+
+@inline(__always)
+func readIndirect(buffer: ByteBuffer, offset: Int, _ byteWidth: UInt8) -> Int {
+  return offset &- numericCast(buffer.readUInt64(
+    offset: offset,
+    byteWidth: byteWidth))
+}
+
+@inline(__always)
+func getCount(buffer: ByteBuffer, offset: Int, byteWidth: UInt8) -> Int {
+  Int(buffer.readUInt64(
+    offset: offset &- numericCast(byteWidth),
+    byteWidth: byteWidth))
+}