Vulkan: Enable framebuffer fetch on SwiftShader Bug: angleproject:6951 Change-Id: I10eeb58be9e8639c0519fc47f327a0894155b755 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3437409 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>