Realtime Compositor: Add evaluator and engine

This patch adds the core realtime compositor evaluator as well as a
compositor draw engine powered by the evaluator that operates in the
viewport. The realtime compositor is a new GPU accelerated compositor
that will be used to power the viewport compositor imminently as well as
the existing compositor in the future.

This patch only adds the evaluator and engine as an experimental
feature, the implementation of the nodes themselves will be committed
separately.

See T99210.

Differential Revision: https://developer.blender.org/D15206

Reviewed By: Clement Foucault

release/scripts/startup/bl_ui/space_userpref.py

@@ -2258,6 +2258,7 @@ class USERPREF_PT_experimental_new_features(ExperimentalPanel, Panel):
                 ({"property": "use_sculpt_tools_tilt"}, "T82877"),
                 ({"property": "use_extended_asset_browser"}, ("project/view/130/", "Project Page")),
                 ({"property": "use_override_templates"}, ("T73318", "Milestone 4")),
+                ({"property": "use_realtime_compositor"}, "T99210"),
             ),
         )