Generate APIs dynamically with `tweaked.cc/index.json`

[tomodachi94]

Is your feature request related to a problem? Please describe.
The custom standard library doesn't know which functions in APIs are real or fake.

Describe the solution you'd like
When the documentation for CC: Tweaked is built, it generates an index.json file. (This is available at https://tweaked.cc/index.json.) This file doesn't contain typings, but it does contain function names.

This wouldn't check for valid typings, but it would make catch a small class of bugs (mistyped function names).

Describe alternatives you've considered
Manually typing function names and types would be error-prone.

Additional context
Add any other context or screenshots about the feature request here.