[Swift] Adds a format file and reformats the swift project (#6250)

* Formats files & adds licence

* Revert arrays

* Keeps array indentation as is

* Adds licence to code formatter

* Updates code generators

swift/Sources/FlatBuffers/Offset.swift

@@ -1,12 +1,28 @@
+/*
+ * Copyright 2020 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
 
 /// Offset object for all the Objects that are written into the buffer
 public struct Offset<T> {
-    /// Offset of the object in the buffer
-    public var o: UOffset
-    /// Returns false if the offset is equal to zero
-    public var isEmpty: Bool { return o == 0 }
-    
-    public init(offset: UOffset) { o = offset }
-    public init() { o = 0 }
+  /// Offset of the object in the buffer
+  public var o: UOffset
+  /// Returns false if the offset is equal to zero
+  public var isEmpty: Bool { o == 0 }
+
+  public init(offset: UOffset) { o = offset }
+  public init() { o = 0 }
 }