Improve GUI behavior when adding multiple torrents

Allows you to bring the main window to the front when one or more "Add new torrent" dialogs are open.
Also allows you to minimize/maximize the "Add new torrent" dialog.

PR #19670.
Closes #17919.

src/gui/guiaddtorrentmanager.cpp

@@ -181,15 +181,12 @@ bool GUIAddTorrentManager::processTorrent(const QString &source, const BitTorren
     if (!hasMetadata)
         btSession()->downloadMetadata(torrentDescr);
 
-#ifndef Q_OS_MACOS
-    auto *dlg = new AddNewTorrentDialog(torrentDescr, params, app()->mainWindow());
-#else
     // By not setting a parent to the "AddNewTorrentDialog", all those dialogs
     // will be displayed on top and will not overlap with the main window.
     auto *dlg = new AddNewTorrentDialog(torrentDescr, params, nullptr);
     // Qt::Window is required to avoid showing only two dialog on top (see #12852).
+    // Also improves the general convenience of adding multiple torrents.
     dlg->setWindowFlags(Qt::Window);
-#endif
 
     dlg->setAttribute(Qt::WA_DeleteOnClose);
     m_dialogs[infoHash] = dlg;