D3D11: Refactor trifan and line loop parameters. Use baseVertex as the parameter of drawLineLoop and drawTriangleFan. The old name is not clear for its usage. BUG=angleproject:1724 Change-Id: I529a157f055eba9d62952093f37eabb8398697db Reviewed-on: https://chromium-review.googlesource.com/430255 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>