PRIMITIVE_RESTART_FIXED_INDEX isn't available until desktop GL 4.3. When it is
not available, emulate it by enabling PRIMITIVE_RESTART and set the primitive
restart index before each draw call based on the index type.

TEST=deqp/functional/gles3/primitiverestart/*

BUG=angleproject:3997

Change-Id: Id736f1056cb07da91c6d592693406333142e6265
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1853885
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>