[Document list] Improve deleting block widgets in nested lists

[oleq]

Part of #11377.

📝 Provide a description of the improvement

Update: I checked this briefly again on the epic branch and it looks better. Perhaps this issue is no longer relevant, needs confirmation.

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In #11346, the handling of delete was improved for lists by leaving everything up to the widget plugin.

This is not always the best strategy, though. It results in a bad UX with nested lists. Take a look:

I'd rather expect the lowest level of the list ("a", "b") to be unaffected and the selection moved to "aa[]" on backspace instead.

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If you'd like to see this improvement implemented, add a 👍 reaction to this post.

[Witoso]

No longer reproducible. Closing.

Screen.Recording.2023-08-24.at.17.12.47.mov