Provide a way to explicitly deselect a room on iPad

[marwing]

Is your feature request related to a problem? Please describe.
When selecting any room, there is (to my knowledge) no way to deselect all again without force quitting the app. This has repeatedly made me accidentally mark a room as read when foregrounding the app because a room was still visible.

Describe the solution you'd like
Add a way to deselect a selected room. As an example, Nheko does this when clicking a selected room again. Alternatively a "back" button could be used, similar to the UI when the screen gets too narrow (like on iPhones), although that would probably feel rather out of place on iPadOS.

Describe alternatives you've considered

Alternative	Problem
Force quit the app every time.	Slow and annoying
Have an empty room marked as favorite (so it's easily accessible) and always open that before backgrounding the app	Even more annoying
Ignore and always manually mark accidentally marked rooms as unread	Also annoying, looses the notification count and sends a read receipt that can't be retracted (in any "normal" client I know)

Additional context
Element Web technically has a similar issue for rooms that aren't in any spaces, so this should maybe be in element-meta?