Change reco: missing text with strikethrough paragraphs

Describe the bug
Based on the discussion in #6168 , here is a follow-up issue.

If a pull request is completely deleted and a change reco is created for it, the diff view only displays the line for which the change reco was created. The rest of the amendment is no longer visible.

However, if the change recommendation is created for the entire amendment, all lines are displayed.

How to Reproduce

1. open a meeting
2. open motions > create a new motion with two paragraphs
3. open the motion > create an amendment on the second paragraph. delete the whole content
4. open this amendment > create a change reco on the first line.

Expected behavior
@bastianjoel and I have discussed a possible solution. Bastians suggestion is that, in this case, the change reco should always be extended to cover the entire strikethrough paragraph, because the change reco is always a replacement and it doesn't make sense to apply a change to just a single line.

Desired behavior: When a change reco is created for a completely strikethrough paragraph in an amendment, all lines are automatically selected and used as the basis for the change.

Reproduce the issue in the web client using the listed meeting, motion, amendment, and change recommendation steps, then trace the diff view behavior for a completely deleted pull request. Done means a change recommendation on a completely strikethrough paragraph automatically includes all lines, while the existing behavior for other amendments remains intact.