Vulkan: enable OES_element_index_uint for Vulkan We already handle 32-bit indices, so this change enables the corresponding extension for ES 2.0. Bug: angleproject:2902 Change-Id: Iccde1d4aac383a9c11edf851778ff315de8d4ad1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1646032 Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: James Dong <dongja@google.com>