Add Saving Root to OnSaving

[Dusty-Sprinkles]

Is your feature request related to a problem? Please describe.

A number of times people have wanted ways to tell when they are saving an object for various reasons, and on a recent issue it was suggested to make a feature request for this, I personally think it would be somewhat useful for some systems that want to clean up assets/reset to a normal state on saving, but not trigger in case of a more general save.

Describe the solution you'd like

Some output of the target hierarchy being saved via the OnSaving node or a different new node with that information (if its heavy to include/would be undesirable to just replace it)

Describe alternatives you've considered

dealing with uncertainty

Additional Context

We could potentially add more information to the saving event which would let you determine the scope of what's being saved. You'd have to make a new issue for this.

Originally posted by @Frooxius in #3228

Requesters

novafox21, krzeszny,
dusty sprinkles/venport

[ProbablePrime]

I took a look at this randomly, There is an IWorldElement "SaveRoot" in scope where this event chain is started.

This seems very doable.

Oh and I just changed the title to avoid confusion.