Desktop,Mobile: Fixes #12744: Fix adding lists to blank lines using toolbar buttons

[personalizedrefrigerator]

Summary

Fixes #12744.

Testing

Automated tests

This pull requests adds the following automated tests:

• In an empty document, with the toggleList command:
  • Verifies that toggleList(ListType.Checklist) adds - [ ] .
  • Verifies that toggleList(ListType.OrderedList) adds 1. .
  • Verifies that toggleList(ListType.UnorderedList) adds - .
• In a document containing an empty block quote:
  • Verifies that toggleList(ListType.UnorderedList) adds - after the block quote markup.
• In a document containing a header, followed by newlines (cursor on the last empty line):
  • Verifies that toggleList(ListType.UnorderedList) adds - to the empty line.

Manual testing

On Fedora Linux:

1. Open the desktop app.
2. Create a new note.
3. Add an unordered list using the editor toolbar.
4. Add four items to the list.
5. Move the cursor somewhere near the middle of the list.
6. Press the "numbered list" button in the editor toolbar.
7. Verify that the item containing the cursor changes to a numbered list item.
8. Undo.
9. Convert the list to a non-tight list — add an empty newline after each list item.
10. Select the list.
11. Press the "numbered list" button.
12. Verify that the list is converted to a numbered list, without adding new list items.

[personalizedrefrigerator]

This bug fix changes the expected behavior for the should not toggle the full list when the cursor is on a blank line test.

• Previously:
  Moving the cursor to an empty line in a non-tight list and pressing a list toggle button did nothing.
• Now:
  The button adds a new list item with the relevant type.