This file changes a lot less than git HEAD. And it should guard against
the same changes. Should reduce the instances of developer confusion
regarding run_code_generation being out of data.

Also update the presubmit check to print a more helpful message in the
case where the code does need to be regenerated.

Bug: angleproject:3333
Change-Id: I190dab5be50fc42512bdfc11c2d200f34f3b2092
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1545123
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>