While waiting for the git mirror to become available we need to clone
these scripts into ANGLE. These scripts are required for the merge
step to work properly.

Bug: angleproject:5114
Change-Id: Ie917149972c8339419b1e3a6d0cf6712fb9888d5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2877011
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>