Vulkan: Allow descriptor pool to allocate different types The internal shaders know exactly what mix of resources they use, so with this change they can make one allocation of multiple types. Bug: angleproject:2958 Change-Id: Ia6f03672b95af4be9618a2f5eeb41ef1c027e810 Reviewed-on: https://chromium-review.googlesource.com/c/1351116 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>