Implement support for the new postprocessing effect system introduced in 5.15.
This should rely on (or at least learn from) the custom material implementation in QTBUG-82245 because many concepts are similar (or the same even).
- depends on
- 
                    QTBUG-82437 RHI: Add postprocessing effects into the rendering -         
- Closed
 
-         
- 
                    QTBUG-82550 RHI: Port post-processing effect system -         
- Closed
 
-         
- 
                    QTBUG-82551 RHI: Port effectlib shaders -         
- Closed
 
-         
- is required for
- 
                     QTBUG-78679
        Port Qt Quick 3D onto the RHI QTBUG-78679
        Port Qt Quick 3D onto the RHI-         
- Closed
 
-         
- resulted in
- 
                    QTBUG-83177 RHI Quick3D: Further work on post-processing effects -         
- Closed
 
-