Vulkan: Translate line loop indices from buffer. When a line loop is drawn with byte indices from a buffer, translate to short. Enable test. BUG=angleproject:2802 Change-Id: Ie178ec866387be85b91291c28e1978db0a09c20a Reviewed-on: https://chromium-review.googlesource.com/1237293 Reviewed-by: Frank Henigman <fjhenigman@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>