Vulkan: Add support for GL_EXT_fragment_shading_rate Add support for GL_EXT_fragment_shading_rate. Bug: angleproject:420310117 Change-Id: I7b368afc45baf8551c222b2569991269117d385b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6726817 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Panfeng Hou <panfeng.hou@arm.com> Reviewed-by: Charlie Lao <cclao@google.com>