Fix-up QR code scanning actions

I cleaned up how resolving QR codes work, I made sure to test both user
and room links and everything works great.

A more awkward bug I fixed is
a workaround around a quirk in Kirigami.Dialog, but actually regresses
QR codes. Because the QR code scanner is currently an extra window (at
least on desktop) the UserDetailDialog will reparent itself to the
soon-to-be-destroyed scanner window.

src/app/roommanager.cpp

@@ -209,9 +209,16 @@ void RoomManager::resolveResource(Uri uri, const QString &action)
         return;
     }
 
-    if (uri.type() == Uri::NonMatrix && action == "qr"_L1) {
-        Q_EMIT externalUrl(uri.toUrl());
-        return;
+    if (action == "qr"_L1) {
+        if (uri.type() == Uri::NonMatrix) {
+            Q_EMIT externalUrl(uri.toUrl());
+            return;
+        }
+        if (uri.type() != Uri::UserId) {
+            uri.setAction(QStringLiteral("join"));
+        } else {
+            uri.setAction(action);
+        }
     }
 
     // For matrix URIs: