The VK_IMAGE_USAGE_STORAGE_BIT has negative performance impact. Right
now we needed for overlay widgets. This CL will only add the bit if we
actually have widget enabled.

Bug: b/157774833
Change-Id: I3027df886c9b34ccfd667152fa4fb090dfadb45b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2225810Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Charlie Lao <cclao@google.com>