Add support for EXT_blend_minmax 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>