Doc: use standard wording in \brief commands

QDoc does some magic with the \class and \namespaces
and \brief commands, so the following wording must be used:
"The xxx class yyy ..."

Change-Id: Id231f30e8464898b776888d5423523de404aae34
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/debugger/stackhandler.cpp

@@ -49,7 +49,8 @@ namespace Internal {
 
 /*!
     \class Debugger::Internal::StackHandler
-    \brief A model to represent the stack in a QTreeView.
+    \brief The StackHandler class provides a model to represent the stack in a
+    QTreeView.
  */
 
 StackHandler::StackHandler()