Update copyright headers (#3086)

Added and updated copyright headers.

Added some missing Flow types.

Removed an invalid prop-types import.

src/utils/patchDOMForGoogleTranslate.js

@@ -1,5 +1,5 @@
 /**
- * Copyright (c) 2013-present, Facebook, Inc.
+ * Copyright (c) Facebook, Inc. and its affiliates.
  *
  * @emails react-core
  * @flow