FrameCapture: Implement capture of coherent bufferstorages. Track buffers with the GL_MAP_COHERENT_BIT_EXT access flag in a CoherentBufferTracker on a per page basis using the PageFaultHandler and protection functions from system_utils. Check for dirty memory and capture it on draw calls. Bug: angleproject:5857 Change-Id: Ib098f96952db7583d3e6517570c179e7754f54b2 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3168629 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>