Add google-java-format-diff.py from the public repository.

Note that the alternate license for this file is already referenced in
the LICENSE file in this folder.

Also add our own trivial launcher script to launch the formatter,
as google-java-format-diff.py expects such a launcher to exist.

Bug: 31552314
Test: Exercised script from new repohook
Change-Id: Ibbbf8a1eb54c73fd6e3d669ed09a4d625536b111
3 files changed