Implement KHR_blend_equation_advanced_coherent * Updated the validation for glBlendBarrier() and ~KHR(). * GL state now includes mBlendAdvancedCoherent. * Updated glEnable() to accept GL_BLEND_ADVANCED_COHERENT_KHR. * It can be queried via glGetIntegerv(), etc. * EXTENDED_DIRTY_BIT_BLEND_ADVANCED_COHERENT added. * Added a corresponding bit to ExternalContextState. * If coherence is supported, there should be no need to use blend barriers, as, based on the spec, the advanced blend ops should then follow order like the basic blend ops. * Relevant tests: *GLES31.functional.blend_equation_advanced.coherent* * On Linux/NVIDIA: From "Not supported" to "Passed" Bug: angleproject:42262258 Change-Id: I7e0e43bdc71524eec111c2d3b024fe73c9795e55 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5634381 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>