Vulkan: Fix scissor clears + enable dEQP tests Vulkan does not support receiving out of bounds numbers for the scissor region but no validation errors are sent. This change clips the region received to fit the current viewport and it fixes many dEQP tests. Bug:angleproject:2356 Change-Id: I5dcf739366ba1f62b56593eaaccedf5f14d0c200 Reviewed-on: https://chromium-review.googlesource.com/957758 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Luc Ferron <lucferron@chromium.org>