Utils: More forward declarations / drop unused headers [T-Z]

Round 1 - focus on headers.
For classes with initial in range [T-Z].

Replace QT_FORWARD_DECLARE_CLASS with QT_BEGIN_NAMESPACE and
QT_END_NAMESPACE and forward declare inside.

Change-Id: I4ac3a8391e6167aa2db3973a9f94a45ac3c8ebd1
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/url.cpp

@@ -28,6 +28,7 @@
 
 #include <QHostAddress>
 #include <QTcpServer>
+#include <QUrl>
 
 namespace Utils {