While this is not exposed to the front end yet, this commit adds support
for creating Compute pipelines for internal usage.

Bug: angleproject:2959
Change-Id: I976eae1ce0f736c257b7b4ae0d1c3b2d9f4da5bb
Reviewed-on: https://chromium-review.googlesource.com/c/1333972
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>