Add kernel object to back end and implement creation and info query.

Bug: angleproject:6001
Change-Id: I6e3fdd2b35d7e73ed56144dc938bf21436d3559f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2922150
Commit-Queue: John Plate <jplate@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>