This CL adds two program pipeline object (PPO) tests based on code
inspection during review.  They are both disabled awaiting fixes.

* The first (DetachAndModifyShader) tests a bug that shaders aren't
detached immediately on call.

* The second (DifferentTextureTypes) tests PPOs with mismatched
texture types. They should not link if the programs use a texture in
non-matching ways.

Test: ProgramPipelineTest31.DetachAndModifyShader*
Test: ProgramPipelineTest31.DifferentTextureTypes*
Bug: b/151462886
Bug: b/151449648
Bug: angleproject:3570
Change-Id: Ief0937397d31c972bf5e3a8d56b02d2dbd5a604b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2146997
Commit-Queue: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>