This extension allows setting independent blend state (and color write mask) for each draw buffer. OES and EXT versions provide exactly the same functionality. It is also included in GLES 3.2 core.

Bug: angleproject:4394
Change-Id: I0c27c419472622e309a038dd1463fa0b3e4ca595
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2078587
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>