Metal: Fix line loop indexes for primitive restart Use the existing code to generate line strips from line loops. Bug: angleproject:401284933 Change-Id: Ie131199c23b93364fabb8f0dc6766f7e8d5f2b8d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6333539 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org> Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com> Reviewed-by: Kenneth Russell <kbr@chromium.org>