This reduces code duplication by including a common set of sources in a
single place. New test sets will be a bit easier to add. It also
encapsulates the dependencies a bit better when we pull the test utils
out of the test targets.

Unblocks a follow-up CL that moves the trace perf test sources into
their own file so we can re-enable optimizations in the main perf test
target.

New warnings popped up in a few of the files because of the new source
set enabling more warnings. This CL also fixes all of those.

Bug: angleproject:3630
Change-Id: Ic30cb30fb4288c4dbbbd29f9bdf04be51e8a6b30
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2103083
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>