Part 1 of the conversion. Mostly renaming js to ts and making sure
things make still sense. Added also handy TS ESLint rules.

In order to support the various .web/.electron/... I ended up adopting
`index.d.ts` as pattern to share type definition. Let me know if that
makes sense for you too. Right now the function type definition is
duplicated, but the solution will be importing from `index.d.ts` and
using `const fn: FnDef = () => ...` that way we can keep all variants in
sync from a single type file.

Such rewrite however is better done in another PR otherwise we risk
confusing git and loosing history (rename + too many changes). Another
thing that might do in the next PR is convert all files to ESModules, as
things get confusing between CJS exports, ESM default/named and TS adds
extra complains.

*   upgrade eslint-plugin-import and fix issues

* Change import ordering

*   enabling no-unused-vars eslint rule

* fix more lint issues

* style: enforce sorting of imports

* style: alphabetize imports

* style: merge duplicated imports

* 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