Add features to optionally increase the LoD offset of all sampling
operations or disable linear filtering. These can be used to compare
performance without recompiling ANGLE.

These features could be potentially implemented in the frontend it is
more difficult because the features are not available at texture
initialization time.

Bug: b/167404532
Change-Id: Ifcf56fbcf130c24c54834737733bbffa5ade3959
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2411475
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>