Debugger: Add special widgets for editing watch values.

Create delegate widgets with validation for bool/int/float
types, using a QVariant-type modelData property.
Also fix register editing to be validated for quint64 values
and editing longer values as hex bigints. Anything else is not
editable.

src/plugins/debugger/watchhandler.h

@@ -122,6 +122,7 @@ private:
     QByteArray niceType(const QByteArray &typeIn) const;
     void formatRequests(QByteArray *out, const WatchItem *item) const;
     DebuggerEngine *engine() const;
+    int itemFormat(const WatchData &data) const;
 
     WatchHandler *m_handler;
     WatchType m_type;