Builds on https://github.com/zed-industries/zed/pull/40794 and
https://github.com/zed-industries/zed/pull/44381

- Fixes the case where creating a new line inside a nested list puts the
cursor correctly under that nested list item.
- Fixes the case where typing a new list item at the expected indent no
longer auto-indents or outdents incorrectly.

Release Notes:

- Fixed an issue in Markdown where new list items weren’t respecting the
expected indentation on type.