Vulkan: drawElements with GL_LINE_LOOP and an offset Also enables a test in LineLoopTest that validates this case. Bug: angleproject:2473 Change-Id: Icb4c5735c11be40cdeceaa051f5a5cef33fd22c6 Reviewed-on: https://chromium-review.googlesource.com/1011669 Commit-Queue: Luc Ferron <lucferron@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>