Quick modifier access for performance scaling

[tavurth]

I was wondering how to disable shadows at runtime, I see that's an option in the ScatterItem node, but I didn't dig through the code enough yet to figure out how it's mapping to the MeshInstances.

Having the ability to modify the modifiers such as count or shadows from code would be very useful for performance scaling optimisation.

Some users may feel OK without shadows displaying, while others with a better GPU will want the whole experience.

This may be related to https://github.com/HungryProton/scatter/issues/64 as with better abilities to modify the instance set it would become quite simple to toggle instance count while running in the editor.

[HungryProton]

Shadows are handled from the Geometry class. Every MeshInstance and MultiMeshInstance inherits from it so it's the same for both. Right now, there's no easy API to change it (apart from looping through all MultimeshInstances and changing the flag there)

I need to work on an easy way to expose all of this from the Scatter node directly, or from an Autoload maybe so you would only have to change this setting once instead.