Per issue 13 in the EXT_external_objects spec, we should request all of
the usage flags that are supported for the format.

Bug: angleproject:3289, angleproject:3389

Change-Id: I5ef9906061af0fd619f580a9f603dd43be162932
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1573218Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>