Use non-separate stencil and blend functions that do not
distinguish between front and back buffers or color and alpha,
if they apply.

This prevents capturing GLES2 functions on GLES1 contexts.

Bug: angleproject:5893
Change-Id: I8303ee5b279268ea9c21e2c6465e1b155d1cc54d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2877238Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>