Store world-specific and dimension-specific permissions data in world/dimension folders

[zml2008]

As in title.

This allows permission configurations to be shipped with worlds, and/or copied around between worlds. Can this be done in a somewhat abstract way?

the file structure would look like:

config/permissionsex/permissions.json -> global
world/permissions.json -> world
world/DIM1/permissions.json -> world + dimension

And any permissions set in a context set that included one or more of those contexts would be written to the appropriate file

Would using the multi-backend (#1924) with sending permissions to a specific file based on contexts work?