Per standard glDisable(GL_DEPTH_TEST) will disable depth write
also regardless of the value of glDepthMask()

Tests done:
- dEQP.GLES2/functional_fragment_ops_depth_stencil_stencil_*_no_depth

Bug: angleproject:2634
Change-Id: I3b101b8c0b3060f5ddbb18d3f97d7d6889cdec01
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1966184
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>