fix(types): build types from JS source

[mcous]

Overview

This PR moves the source of truth for typing from a separately maintained types/index.d.ts file to JSDoc comments in src. I'm hopeful this will ease the maintenance burden of types, especially as we're supporting three major versions of Svelte.

Svelte itself is undergoing some major-ish typing changes, so I'm keeping this as a draft for now

Change log

• Move JSDoc comments from types/index.d.ts to src/**
• Add types build step with tsc and enableJs

Future work

For now, I think vanilla JS is the best fit for this project, so I don't see any compelling reason to do anything drastic like switch to TS and introduce a build step. That being said, I do see this as a potential first step in introducing type-checking to the codebase via TS's checkJs option

[github-actions[bot]]

:tada: This PR is included in version 5.2.0-next.2 :tada:

The release is available on:

• npm package (@next dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[github-actions[bot]]

:tada: This PR is included in version 5.2.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: