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
TEST=angle_end2end_tests:ProgramInterfaceTestES31.*
Change-Id: I5128cda43b0d9176c910b036cdc76bf37757670e
Reviewed-on: https://chromium-review.googlesource.com/474212
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
