With the new SceneTreeFTI, most xforms are updated to the server externally by the FTI system, so it is no longer necessary to update the server on each NOTIFICATION_TRANSFORM_CHANGED.

Each call to VisualServer::get_singleton()->instance_set_transform() incurs some expense, so it is sensible to reduce these when they are superfluous (as a later update will be made by SceneTreeFTI immediately prior to rendering).

Notes

• I didn't put this in the main PR both to keep it clear and free from excessive optimization, and because I wanted to look at this in isolation. There is the potential for regressions here so we can easily revert or bisect a self contained PR.
• With the old FTI I had previously looked at preventing propagation into non-interpolated branches ([3.x] Physics Interpolation - reduce xforms in non-interpolated nodes #103331) but with the new technique this is probably no longer appropriate, not least because we need to set DIRTY_GLOBAL_INTERPOLATED.
• Most of these NOTIFICATION_TRANSFORM_CHANGED will be no-ops for VisualInstances in this situation (which isn't ideal), however we need to (for now) allow any derived classes the opportunity to respond to the notification. This can possibly be further optimized in the future.