Motion > amendment: formatting change in amendmend plus original text leads to wrong diff

[MSoeb]

Describe the bug
If an amendment change also includes a formatting change in amendment and original text, the diff will be wrong displayed. The whole paragraph will be shown as diff not the relevant parts.

Original motion:

Amendment with red marked diff (amendment plus original text):

Outcome view:

How to Reproduce
Steps to reproduce the behavior:

1. open a meeting
2. open motions > create a motion > create an amendment and change one word. mark the new word and an original word in bold. > save diff
3. visual should now be broken like in the example above

Expected behavior
If an amendment contains text and fomat changes, the diff visual should clearly display differences and should not show the a change in the whole paragraph.

This issue is part of the Meta Diff issue. #2956