very very hacky

related to #60163

Support odd indentation sizes (fixes #17639)

Fixes #47537

Use our own version of markdown named headers. This fixes some bugs around handling duplicate headers

Fixes #59711

For a md document:

```md
# a

# a

- [a](#a)
- [next a](#a-1)
```

You can now click on the second link in the editor to navigate to the second `a` header. It is identified by being suffixed with `-1`.