typedoc/dartdoc/etc support

[cabljac]

This has been mentioned a few times, and would be a nice feature.

It could be done in various ways:

1. using typedoc-markdown-plugin to generate .md files, and formatting them from here (would have to do this for each language, and probably quite prone to errors imo)

2. writing our own plugin for typedoc etc (this is what docusaurus do, but potentially a lot of effort)

3. write some kind of parser of various generated json files into a common format for docs.page (potentially also a lot of effort)

[cabljac]

Began work on this here https://github.com/invertase/docs.page/tree/typedoc-cli

Remaining tasks for typedoc support:

• [x] - error catching (missing config options etc) on dart_cli
• [x] - make sure live preview mode doesn't break with it
• [x] - make sure references works with locales
• [x] - generate a nicer references/index.mdx and also make sure it doesn’t overwrite existing file
• [ ] - add docs for everything
• [ ] - manually test for any obvious breaking changes

Hoping dartdoc will be quite easy to add in once this is done.