Note: GL_TEXTURE_COMPARE_MODE=GL_NONE is not supported on shadow sampler
for now.

Bug: angleproject:2634
Change-Id: I470bad6322e78ef1408e4334e1e778821df7cbf1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2433332
Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>