Remove some lambdas from Utils::transform calls

It is often possible to user (member) functions or members directly.
That improves readablility and potentially reduces the total number of
symbols.
Also use qobject_container_cast at places where it is appropriate.

Change-Id: Ia2591bca356591e001e2c53eeebcf753e5bc3c37
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/coreplugin/mainwindow.cpp

@@ -353,10 +353,7 @@ void MainWindow::closeEvent(QCloseEvent *event)
 void MainWindow::openDroppedFiles(const QList<DropSupport::FileSpec> &files)
 {
     raiseWindow();
-    QStringList filePaths = Utils::transform(files,
-                                             [](const DropSupport::FileSpec &spec) -> QString {
-                                                 return spec.filePath;
-                                             });
+    QStringList filePaths = Utils::transform(files, &DropSupport::FileSpec::filePath);
     openFiles(filePaths, ICore::SwitchMode);
 }