Vulkan: add tests for clearing/drawing after invalidate Two tests, to ensure that: - Clear gets treated as a LoadOp instead of as an out-of-renderpass clear, even if draws don't touch color buffers. - Invalidated image gets contents marked as defined after invalidate+clear, so draws to it get a renderpass with LoadOp=Load Bug: angleproject:7127 Change-Id: I78a8bd2100ba941a74755402649ae8edc7978026 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3552090 Reviewed-by: Jamie Madill <jmadill@chromium.org> Auto-Submit: Steven Noonan <steven@valvesoftware.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>