bug(markdown) Oddities with nested lists

Describe the bug
Based on markdown

- Bulleted item
  1. Numbered item

Shown in RT mode.

1. Selecting the numbered item shows both the bullet button and the number button selected. This may or may not be expected, as it is technically within a bulleted item. Pressing the number button removes the number, as expected.
2. Unexpectedly, pressing the bullet button also removes the number. Pressing it a second time removes it from the parent bulleted item, as expected.
3. You cannot backspace out of the first item in the list, but a second item (with nested list underneath) can be backspaced. Ideally would be consistent.

More generally, if we support a numbered list under a bullet list (as we do in MD, and can transform this to RT), this should be achievable in RT mode without having to go to MD mode to do it.

Screenshots

Desktop (please complete the following information):
Windows 11 Chrome 103

Additional context
https://meta.stackexchange.com/a/380396/51

Reproduce the nested-list example in RT mode using the Markdown snippet from the issue, then compare the numbered and bulleted toolbar behavior and backspace handling with the corresponding MD structure. Done means nested lists can be edited in RT mode consistently without removing the wrong list or requiring a switch to MD mode.