Add API entry and validation checks(GLES 3.1 section 7.3).
Add the first 2 interfaces(PROGRAM_INPUT and PROGRAM_OUTPUT) implementation.

BUG=angleproject:1920

Change-Id: Ib2dedded9fd79b315e9f38de7c27a5e4ec4c6066
Reviewed-on: https://chromium-review.googlesource.com/453085
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>