The open full player swallows Enter and Escape in notes #467

While the full player is open, a note's own keys stop working: in the find bar, Enter (next match) and Escape (close) don't reach the note.

Reproduce (found by UI2 live on Obsidian 1.14.4 while building #466; reproduced on master)

1. Open the PodNotes full player.
2. In a markdown note in another pane, open the find bar (Ctrl/Cmd+F) and type a search.
3. Press Enter or Escape: nothing happens in the note.

Cause: the full player registers its keys on a Scope pushed above the workspace scope, so it takes Enter and Escape even when focus is in a note. This came in with the v3 shell (#434), which is not released yet. 2.21.1 doesn't have it.

Expected: player keys work only while focus is in the PodNotes view. Notes, the find bar and other views get their keys. Fix by registering the player's keys on the view's own scope (or by checking focus), not on a global scope above the workspace.

This must be fixed before 2.22.0, because otherwise the release would break keyboard use in notes whenever the player is open.