Enabling transform feedback can affect which draw modes are valid. We
can use the exiting draw modes cache to save having to check the draw
modes twice. We update the cached draw modes on any change to the
transform feedback activity state. e.g. when transform feedback is
started, or resumed.

There are also spec changes that comes into effect in ES 3.2 or when
EXT_geometry_shader is enabled. Again we cache these draw modes in the
packed valid draw modes map.

Will allow for faster validation for draw calls once the other checks
for transform feedback are optimized. Also adds a new regression test.

Bug: angleproject:2966
Change-Id: Iab901e45aab70980b9e631ec8383fdeadbd32368
Reviewed-on: https://chromium-review.googlesource.com/c/1357149
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>