Newlines not handled properly when inserted through a smart picker

[kyteinsky]

Describe the bug
Text inserted from a smart picker that contains multiple newlines is not handled properly.
See original issue: nextcloud/text_templates#13
Related issue: #593

To Reproduce
Steps to reproduce the behavior:

1. Insert text from smart picker that has multiple newlines, eg. using the text_templates app
2. Try to delete one newline from the bunch of consecutive newlines
3. See issue that all newlines in the document are condensed

Expected behavior
Newlines remain intact on modification.

Screenshots
Courtesy @sptcguy
https://github.com/user-attachments/assets/270c6819-235a-4015-984e-31fc3f458237

Server details:

• Nextcloud version: 31.0.0
• PHP Version: 8.1
• Database: MariaDB 10.5

Client details:

• OS: Linux
• Browser: Chromium/Firefox
• Browser version: 128
• Device: desktop