As we have done for default uniforms and textures, we should cache
descriptorset for driver uniforms to avoid repeatedly create them.

Bug: b/161750230
Change-Id: I0afabb226d5a8e8c7838fa2484ec7f9689ed5fa0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2309349Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Charlie Lao <cclao@google.com>