Program interface queries are a generic way to query attributes of
the program like uniforms, samplers, attributes, etc. This change
supports those queries for program outputs.

Bug: angleproject:3596
Test: dEQP-GLES31.functional.program_interface_query.*
Test: ProgramInterfaceTest.cpp
Change-Id: I0f13692949073b45988b6f930eee9eaa6411bbe2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1801998
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>