`./build decl` now builds TS declarations for everything exported by
`sim/`. Unfortunately, the built TS declarations still refer to global
types, so some things still have `any` type, but it's much better than
nothing.
This fixes a bug where `.config-dist/custom-formats.js` wasn't getting
deleted when `config/custom-formats.ts` was deleted.
This also cleans up some other clutter in `.config-dist`.
Previously, if you deleted a file from `data/mods/`, it wouldn't also
get deleted from `.data-dist/mods/`. This fixes that, and the
corresponding issue in `server/chat-plugins/`.
For reasons of performance and/or laziness, I've chosen to only clean
those two directories, not all built directories.