GNOME Mutter 51.rc Adds Cross-GPU Buffer Scan-Out Support, Other Last Minute Work

The release candidates are out today for the GNOME Shell and Mutter in preparing for the formal "GNOME 51.rc" release in the coming days. Both Mutter and GNOME Shell tagged their 51.rc releases today. Arguably most notable with the release candidate for GNOME Mutter 51 is adding cross-GPU buffer scan-out support. An automatic test will be done in trying to attempt to perform cross-GPU buffer scan-out support for better efficiency with multi-GPU setups such as for hybrid laptops. This builds upon other recent improvements to GNOME for direct scan-out. This release candidate also adds stylus eraser button configuration support, support for Night Light mode on hardware without GAMMA_LUT abilities, and support for overriding the client initial configuration. Mutter 51.rc also adds a background effect policy for client-requested background blur support. The default is a blur radius 24, saturation 1.25, and noise 0.015. But GNOME Shell or other shells will be able to provide their own visual parameters for this background effect policy if so desired. On the fixes side is a fix for using the hardware cursor for SVG cursors, fixes multiple monitors being reported as the primary monitor, desaturated SDR content in HDR mode, fixing a possible hang on external monitor hot-plugging, and fixing direct scan-out for captures without DMA-BUF. Mutter 51.rc also fixed various memory leaks and crash fixes. More details on these latest Mutter changes via this commit. Over on the GNOME Shell 51.rc side, the Rust-based Glycin library is now being used to load and cache background images. There is also fixes around direct scan-out usage and a variety of other fixes. Those details in this commit.