Vulkan: implement primitive restart Implements ES 3.0 feature GL_PRIMITIVE_RESTART_FIXED_INDEX, which allows the application to use a fixed "restart" index to restart the primitive during a single draw call. This change does't handle GL_LINE_LOOP primitives, which requires a bit of special handling. Bug: angleproject:3215 Change-Id: I2388852683fd17328a6a76c48d70a24d67ce8b67 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1650301 Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>