Fix invalid enums for OES_draw_buffers_indexed Make sure the new enums are invalid before the extension is enabled. Add a angle_end2end_test for that. Bug: angleproject:4394, chromium:1058744 Change-Id: Ib88f6159294dab2eb7d3662b96c44424ab132782 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2205179 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Shrek Shao <shrekshao@google.com>