[pseudoIDs] More pseudo ID fixes - Part 2 (#3181)

Fixes include:
- Translating state keys that contain user IDs to their respective room
keys for both querying and sending state events
- **NOTE**: there may be design discussion needed on what should happen
when sender keys cannot be found for users
- A simple fix for kicking guests from rooms properly
- Logic for boundary history visibilities was slightly off (I'm
surprised this only manifested in pseudo ID room versions)

Signed-off-by: `Sam Wedgwood <sam@wedgwood.dev>`

roomserver/internal/input/input_events.go

@@ -933,12 +933,7 @@ func (r *Inputer) kickGuests(ctx context.Context, event gomatrixserverlib.PDU, r
 			return err
 		}
 
-		userID, err := spec.NewUserID(stateKey, true)
-		if err != nil {
-			return err
-		}
-
-		signingIdentity, err := r.SigningIdentity(ctx, *validRoomID, *userID)
+		signingIdentity, err := r.SigningIdentity(ctx, *validRoomID, *memberUserID)
 		if err != nil {
 			return err
 		}