When calling EndTransformFeedback, we might change the current program.
This sets a dirty bit, but it might not get cleared before the next
draw call, so this change makes us manually restore the program state
after calling EndTransformFeedback.

This is a follow-up to:
https://chromium-review.googlesource.com/c/angle/angle/+/1448661

Bug: 832238
Change-Id: I1bea1b9685f55d68b04439a9b0a305deb48708c0
Reviewed-on: https://chromium-review.googlesource.com/c/1475061
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>