alphaReference is not used. It previously provided a configurable
threshold for alphaToCoverage, before that was explicitly managed by
pipeline state.

The sample mask is not dynamic state, so it can never change between
draws without a complete context change.

sRGB write control is not context state, it is determined by the image
view format.

Bug: b/118386749
Change-Id: Id631732fad52cf6b75c1635bcd7ef464dda10e54
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29649Tested-by: Chris Forbes <chrisforbes@google.com>
Presubmit-Ready: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>