Vulkan: Allow dither for some color blend modes Some color blend modes are known to work with our dither emulation. Test: Candy Crush on Pixel 6 Bug: b/232574868 Change-Id: I1b57e243afcf4643e2cd12f862408050751fa987 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3780846 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>