D3D11: Avoid GLenum conversions in GetBlendStateKey Bug: b/300968773 Change-Id: Ia41f77e686e0f1afc91381e29334f73859868129 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5009815 Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>