This is to add additional modes (MIN, MAX) to "BlendEquation".
- add cases for "GL_MIN" and "GL_MAX" into "PackGLBlendOp()" in
vk_cache_utils.cpp
- add enabling "blendMinMax" codes into vk_caps_utils.cpp

And, AUTHORS and CONTRIBUTORS are updated.

BUG=angleproject:2897
Tests: dEQP-GLES3.functional.fragment_ops.blend.*min*
       dEQP-GLES3.functional.fragment_ops.blend.*max*

Change-Id: I13a1d6d28a104b18e21697f9f23d77e4eda2d1a6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1621582
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>