WYSIWYG editor doesn't support nested lists

[u9000-Nine]

Describe the bug

Pressing Tab in a list in the WYSIWYG editor moves focus to the next button instead of creating a sublist.

Reproduction

1. Enable the WYSIWYG editor (the Aa button in the input box).
2. Create an ordered or unordered list.
3. Make a list item with text.
4. Make a second list item, but press Tab before writing any text.
5. Observer that focus is moved instead of creating a sublist.

Expected behavior

When in a list, Tab and Shift+Tab change the level of list, and pressing Esc is needed for Tab to move focus.

System info

OS: Windows 10
Browser: Helium 0.9.4.1
Cinny version: v1.11.1 PWA