Making the `crdt` package fully TypeScript-strict.

This PR has no functional changes. Only types are changing and getting
improved (more stricter).

A follow-up PR will come next that does a few functional changes to make
this package fully strict.

actual-server does not need to import the full actual-app/api package.
It can import only the CRDT stuff.. so I'm extracting it into a new
package to reduce the size of actual-server and make the link between
things more transparent.

This PR converts everything (aside from electron) from CommonJS to ESM.
It is needed to reduce the changes that will happen during the migration
to Typescript (as TS does not play nice with CJS).

Basically:
- rewrite `require()` to `import`
- rewrite `module.exports` to `exports`
- introduce `ts-node` to run importers so we can convert them to TS too

Lastly, sorry for this larg-ish PR, not my preference but when I tried
to reduce its scope, I would end up with mixed commons/esm that was even
more tricky to handle.