Following on from #1146 this PR removes all unused exports from
`loot-core/`

- Enforce that imports from the same package are merged into a single
import
- In `loot-core`, require that imports of other `loot-core` files use a
relative import (like the vast majority of such imports) rather than
specifiers starting with `loot-core/` (probably a result of moving files
out of other packages into `loot-core`)

Another batch of `loot-core` migrated.

* style: enforce ordering of imports

* style: sort imports in loot-core

* style: sort imports in desktop-client

* style: sort imports in loot-design

* style: manual fixes