EditorChangeHandler doesn't handle all change types

[peppy]

It is not aware of changes outside of hitobjects. Also, since it's using a legacy encoder it is unaware of new elements in hitobjects which are not supported by the legacy format.

This can be seen on the timing screen, where changes to ControlPoints do not trigger state saving.

We either want to update this to use json serialisation/patching, or implement a more custom object equality based approach. The first option is simplest but performance may be an issue.

[peppy]

Priority should be given to this for control points specifically, as it can be very frustrating when trying to time a beatmap.