FrameCapture: Use gl*Separate functions only when required. 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/+/2877238 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>