- building brand new content is probably interfering with how iOS syncs up delivered and seen notifications between devices
- simplify all the various steps and make the flows easier to follow
* Extract notification content building outside of the NotificationItemProxy. First step in a bigger refactoring of the NSE
* Import the attributed string buider into the NSE, sort `sources` imports
* Extract message event string building into the RoomMessageEventStringBuilder and reuse it building content for push notifications
* Cleanup
* Add changelog