Properly apply custom materials with CanvasGroups in the GLES3 backend
Properly blur backbuffer when using a partial rect in forward_plus and
gl_compatibility renderers
Properly set fit_margin when clear_margin is set
Fix shader error during backbuffer clear in mobile renderer
This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
