Migrating complex grid layout settings

[steve-crook-wtg]

I'm looking at adding some new Block Grid Settings Migrators, because the only one there at the moment is for the boolean view. (The full list of grid layout settings views is here)

textstring, textarea and number are all easy, because they can use fixed, existing data types. Next up is radiobuttonlist. To add a setting for this to a Block Grid settings doc type, I'll need to create a new radio button list data type with the prevalues from the JSON config. I've managed to extract the prevalues, but I'm having some trouble figuring out how to build and refer to another new data type while in the middle of doing the grid layout data type conversion. Is it possible to generate a data type without a corresponding source XML file, preferably utilizing existing data type migration code? I haven't been able to find another example of this in the Migrations code.