Vulkan: prepare for ES3 This makes ES3_VULKAN() pass the instantiability test, allowing it to be specified in end2end tests. Bug: angleproject:2950 Change-Id: Ife70a22fb8193f9eebe64bec491a24b47bc76939 Reviewed-on: https://chromium-review.googlesource.com/c/1325729 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>