Add support for the remaining functions for OpenCL 1.2 for the
front end and pass-through back end.
Also fix several bugs discovered by the conformance tests.

Bug: angleproject:6015
Change-Id: I1dca1c3f4c1d9aea7f0501094c171116ea01381f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2954259Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: John Plate <jplate@google.com>