feat: implement typescript declaration files

[earthernsence]

This pull request aims to close issue #150 and replace pull request #204. To do this, we can simply use the native TypeScript compiler to generate the declaration files, which seems to work pretty much identically to the bili changes used in #204, but it (to me) feels a bit more natural.

I guess the other thing that would need to be figured out before this is merged is how we want community notations to work. Currently, they are made to be installed separately from the main package, which is mostly fine for most use cases. It becomes a bit more complicated when there are types involved (and if somebody wanted to use the community notations in, say, a React/Vue application that wants to use the NPM versions of the packages).

As a note: the build-test.yml file can be removed; it was simply how I tested that the build wouldn't fail because it wasn't working on my machine.

[earthernsence]

Also worth mentioning: on my fork, I also tested using the bili changes (though as I said I couldn't get the build step to work properly) and using a new bundler called parcel. Those branches are available on my repository. parcel would likely be a really big change and fundamentally alter how we handle building, but it's more supported than bili nowadays (bili doesn't even have working documentation). This is why I feel that the tsc option is more natural and better-suited for long-term support.