Search support for room version upgrades

[lampholder]

Search was descoped from #7164 so that it could be considered separately.

[lampholder]

This could be solved front end or back end.

If we're solving it front end, I'd suggest we:

• when we execute a search from the UX, check the room state to see if there's a historical version of that room
• if there is, add that room to the list of rooms specified in the search API request
  • n.b. we only go on room back - don't start traversing the whole history of room versions (this decision made for ease - if it's easy to traverse all of the room version chain without introducing complexity/potential for UX failure then do that)
• I expect we'll then see the search results rendered as if the user searched for all rooms (in which the per-day results are headed with Room: Room Name
  • If we're rendering a room name atop results from old versions of the room, we should:
    • pretend that the room name is the same as the current name (using whatever happened to be the old version's name at tombstone time is likely to be confusing)
    • decorate the room name with a low-attention (v1) suffix

[anoadragon453]

This has been solved on the server-side :)

Let us know if it's still unclear in any way.