Conversion of I:R areas as CK3 de jure duchies

[IhateTrains]

For now just saving so I don't forget. May get to this once AUH compatibility is stable.
https://discord.com/channels/612683871112396800/692883287336681592/1471619950190923847
https://discord.com/channels/612683871112396800/692883287336681592/1471627995746799730
https://discord.com/channels/612683871112396800/692883287336681592/1471642336130764935
https://discord.com/channels/612683871112396800/692883287336681592/1472346330604109895
https://discord.com/channels/612683871112396800/692883287336681592/1472350186612461823
https://discord.com/channels/612683871112396800/692883287336681592/1472357412349673634

[IhateTrains]

results of a test with a duchy capital changed:
https://discord.com/channels/612683871112396800/692883287336681592/1472445040956805346

[IhateTrains]

Once de jure duchies are set up this way, we should also try removing the gap filler de jure kingdoms and empires (for example heritage empires). Maybe they really don't need to cover the whole map as of CK3 1.18.

Problem with de jure drift:
https://discord.com/channels/612683871112396800/692883287336681592/1472445045230800906