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: Ide7d5ad40a611a091c3dffab47fd31da57b69f1d
Reviewed-on: https://chromium-review.googlesource.com/457523
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>