Migrate markup from D7 to D8

Alright, I just tested the patch. This still needs further work as it only migrates the field itself and the widget and formatter, but NOT the markup itself! Also a formatter is missing.

I give up.

No idea how to migrate the markup_field settings properly from d7 to d9. At first, I thought, I could eventually map it through "defineValueProcessPipeline", even if this is used for content per field_instance. I thought it might also map the "default" value for the field.
But I guess that this was the wrong approach.

My next approach was, to create a "markup_settings.yml" inside "markup/migrations/", which I thought could map the field settings! But now I think this is only used for global settings which need mapping. Not per field settings. I am honestly out of ideas, and the whole migration business isn't properly documented (or I just can't google correctly).

A good example, found in core, is the core module "text". Maybe someone else knows the correct approach and can show me an example.