We could expand this functionality in the future to only update the
pipeline when a signficiant bit of pipeline state changes. For now this
is mostly a proof of concept.

Significantly improves performance in the textures microbenchmark.

Bug: angleproject:3117
Change-Id: I3957dd2f08d7d89694f94ddbe45eeeeb620bac0a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1650790Reviewed-by: Tobin Ehlis <tobine@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>