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/qmakeprojectmanager/qmakeparsernodes.cpp

@@ -362,7 +362,7 @@ void QmakePriFile::update(const Internal::QmakePriFileEvalResult &result)
 void QmakePriFile::watchFolders(const QSet<FileName> &folders)
 {
     const QSet<QString> folderStrings =
-            Utils::transform(folders, [] (const FileName &f) { return f.toString(); });
+            Utils::transform(folders, &FileName::toString);
     QSet<QString> toUnwatch = m_watchedFolders;
     toUnwatch.subtract(folderStrings);