Vulkan: Enable custom border colors on SwiftShader This extension can now be enabled on SwiftShader after bug fixes that landed in https://swiftshader-review.googlesource.com/c/SwiftShader/+/64688 and https://swiftshader-review.googlesource.com/c/SwiftShader/+/66148 Bug: angleproject:6200 Bug: b/227518327 Change-Id: I65fb342a96c47b1ea5ba2ee773c8ae5539052b94 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3569585 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>