Compositor: Replace resolution concept by canvas

This is a code refactor in preparation of supporting canvas
compositing. See {D12466}.

No functional changes, all canvases are at (0,0) position matching
tiled implementation.

Differential Revision: https://developer.blender.org/D12465

source/blender/compositor/operations/COM_TrackPositionOperation.cc

@@ -157,11 +157,9 @@ const float *TrackPositionOperation::get_constant_elem()
   return &track_position_;
 }
 
-void TrackPositionOperation::determineResolution(unsigned int resolution[2],
-                                                 unsigned int preferredResolution[2])
+void TrackPositionOperation::determine_canvas(const rcti &preferred_area, rcti &r_area)
 {
-  resolution[0] = preferredResolution[0];
-  resolution[1] = preferredResolution[1];
+  r_area = preferred_area;
 }
 
 }  // namespace blender::compositor