Add EXT_texture_mirror_clamp_to_edge entry points Bug: angleproject:7968 Change-Id: I04b0c5d7b5148fbaca24d77a2c8688ea7a96cb64 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4262073 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com> Auto-Submit: Alexey Knyazev <lexa.knyazev@gmail.com>