Vulkan: Fix border color adjustment for emulated formats Emulated opaque ETC compressed formats are decoded to RGBA8 so the border color must have its alpha as one. Generalized AdjustBorderColor to enforce opaque alpha for opaque formats and to support both ways, in which ANGLE could emulate LUMA formats. Moved AdjustBorderColor to renderer_utils so it could be used with other backends. Bug: angleproject:5978 Change-Id: I9ec44444fd373b1ca6116ebc4447063a014025ce Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4265514 Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>