The functions weren't properly exposed from the
EGL_ANGLE_feature_control extension.

Bug: angleproject:1621
Change-Id: Ie91a18966a84db88d6a9a555e75cba8cea0a6521
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1688498
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>