The extension EGL_ANGLE_iosurface_client_buffer adds a new attribute
to the config: EGL_BIND_TO_TEXTURE_TARGET_ANGLE. However, validation
was not checking the extension was present when this attribute was
requested.

Bug: chromium:1015454
Change-Id: I24c6e20f3b602e8a71a46f0f1e99c1472d5bbb1e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2078892
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>