Instead of using uniform, use flip/rotation specialization constant when
available. This allows matrix multiplication calculated at compile time
instead of shader execution time.

Bug: angleproject:4901
Bug: angleproject:3589
Change-Id: I5a8a82b1cffbbbeba2617cb7e9a0ec38f9984d50
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2530457
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>