Edited message gets truncated but full message is not reachable on second devices

[nicodh]

It seems when a message is longer than the DC_DESIRED_TEXT_LINES or DC_DESIRED_TEXT_LINE_LEN threshold AFTER editing, it gets truncated, but mime_modified (which is true then) is not persisted in save_text_edit_to_db.

This results in a truncated message where the full message is not reachable (has_html return false) on other devices

This does not affect the device where the message is edited, as send_edit_request does not parse and truncate the updated message at all. Only other devices are affected.

A solution would be to update mime_modified in save_text_edit_to_db and to perform the same truncate_msg_text handling as with new messages, although this could result in a message that is not editable anymore after updating it due to #6564

Steps to reduce:

1. create a message on a multi device account
2. edit the message and paste enough text to exceed the long message threshold
3. see on another device the text being truncated but no "Show full message" button appears to show the full message

Related:
#7749
#7718
#7791
deltachat/deltachat-desktop#6384