Prefix the files with angle_ to disambiguate them from other tools.

Bug: b/168736059
Change-Id: I7be25ca18fb69d7f2ab71bdf355932865d134954
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2425197
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>