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: I50057f7b99f4dc7c23ca87fa9b797ca424f66e3d
Reviewed-on: https://chromium-review.googlesource.com/475075Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>