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

Bug: angleproject:6001
Change-Id: If94db8ab8b491e1ac21c767347cabb6f4f3b3cba
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2912465Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: John Plate <jplate@google.com>