Not escaping the list item when at the start of code block

[CatStrategist]

Steps:

1. Create a list item
2. In this list item add codeblock
3. Type foo
4. Put the cursor at the beginning of the text - []foo
5. Press backspace

Expected:

List item is removed.

Actual:

Nothing happens, backspace for removing list item works only if you first remove the whole text.

Screencast:

0_list1.mp4

Originally posted by @FilipTokarski in #11377 (comment)

[CatStrategist]

@FilipTokarski What's the browser/OS? I use chrome@macOS and it works fine

Nagranie.z.ekranu.2022-03-31.o.16.59.44.mov

.

[FilipTokarski]

This behaviour is caused by the Text part language plugin. If you remove it from the build, everything works fine.

[arkflpc]

Root cause: CodeBlockEditing added codeBlock element to model with language attribute. TextPartLanguageEditing was triggered by this attribute and added span around codeBlock which wasn't expected by DocumentListEditing's downcast. So the list was outdented correctly in the model, but view retained <ul><li>...</li></ul>.

Possible solution: Downcast in TextPartLanguageEditing should ignore language attributes when the item is neither $textProxy nor documentSelection