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/textfieldcombobox.h

@@ -32,9 +32,11 @@
 namespace Utils {
 
 // Documentation inside.
-class QTCREATOR_UTILS_EXPORT TextFieldComboBox : public QComboBox {
+class QTCREATOR_UTILS_EXPORT TextFieldComboBox : public QComboBox
+{
     Q_PROPERTY(QString indexText READ text WRITE setText)
     Q_OBJECT
+
 public:
     explicit TextFieldComboBox(QWidget *parent = nullptr);