RPGCore.DataEditor support for data variants

[fydar]

Add support for authoring data variants to the RPGCore data editor.

Data variants should adopt a standardized format such as JSON Patch.

The data editor will need to support reading JSON or XML paths to determine what data needs to be changed as apart of the patch.

Patches should also be optimal; they should include no instances of data being added and then removed.

There should be APIs to apply the patches to the original file, as well as APIs to unpack the variant file. I would like to take inspiration from the nested prefab system in Unity.

Using patches saved over time could be used for change tracking to inform an undo/redo system.

Generating patches from diffs generated by source control could also be useful for previewing changes made to files and creating custom merging tools.