Search in multiple manually selected Rooms or Spaces

Is your suggestion related to a problem? Please describe.

Very often we need to find some message and can't remember in which exactly room it was posted, but remember the possible list of rooms (community). At now Element provide searching only in single room ("This room") or in all rooms.
And there is no way to search in custom list of rooms, only repeat search in each separate room manually.

Describe the solution you'd like.

At now we have Spaces, that groups rooms by community or any custom private grouping. Will be good to add feature for search in all rooms of current space to Element, for extend the searching capabilities.

Additionally, the search interface can be extended by selecting rooms manually from list of all rooms.

The issue does not identify implementation files, tests, or an entry point. Start by locating Element's search interface and its handling of Spaces and room filters; the work is done when searches can target all rooms in a Space and a manually selected set of rooms, with coverage for both selection modes.