feat(developer): implement a in-memory model for kmc-convert 😎

[SabineSIL]

Kmc-convert will allow to convert between various common keyboard description file formats.

The first/present conversion of kmc-convert converts .keylayout files into kmn files using an array of Objects for data exchange.

The future kmc-convert should use an in-memory-model that can be used for all conversions.

This is an idea of implementation for the future kmc-convert:

https://docs.google.com/document/d/12J3NGO6RxIthCpZDTR8FYSRjiMgXJDLwPY2z9xqKzJ0/edit?tab=t.0#heading=h.du7xg0kgc2oi