Dither is technically not a part of blend state so it was removed from there as a first step towards exposing OES_draw_buffers_indexed (that defines independent blend state for each draw buffer).

Rasterizer state seems to be the closest (although also not accurate) place for it to keep code changes to a minimum. ANGLE's D3D11, Vulkan, and Metal renderers ignore dithering altogether.

Bug: angleproject:4394
Change-Id: Ib138624b9218851d18cd63e2033e8e8ac8ca71d9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2050464Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>