Before this change, Ctrl+PgUp/PgDown didn't select the next room, but
actually moved two rooms at once because the signal handler was called
twice. I'm not entirely sure why this happens (it might be a bug in a
lower layer?), but as we don't want to handle the same event elsewhere,
accepting the event doesn't feel wrong and it appears to fix the issue.
So let's just do that.
BUG: 459997
Update linkpreviewer to minimise the number of resizes.
- There is now a placeholder loading element to hold space while the data is obtained
- The component starts with a set size but can be expanded to see the whole item.
- The expand/contract button is only visible on hover
- The default size is picked to show 3 lines of text (1 heading and 2 description, 2 heading and 1 description, etc)
This is designed to help with the timeline scroll jumping CCBUG: 463235 by minimizing the amount of resizing for items in the timeline.
Before

After when compressed

After When expanded

After Loading

Implement folding sections for multiple consecutive state events. This also reworks some of the aggregated text output:
- Only new days cause a new section
- The aggregated text starts with either a single username or n users
- If the same user did the same action mutltiple times it will be in the aggregated text a user did x n times
- When there are multiple authors in a block with multiple state event types it will use or rather than and before the last event. e.g 3 user left the room or joined the room.
Folded

Unfolded

Implements network/neochat#90