Doc: Add example categories for Active Qt examples

Task-number: QTBUG-116039
Change-Id: I171566bea939dc6a801e5b3dc441b814693d8d79
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>
(cherry picked from commit ba7dbbb711)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/activeqt/comapp/doc/src/comapp.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example activeqt/comapp
     \title COM App Example (ActiveQt)
+    \examplecategory {Desktop}
     \ingroup activeqt-examples
 
     \brief The COM App example shows how to use ActiveQt to develop a Qt

examples/activeqt/qutlook/doc/src/qutlook.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example activeqt/qutlook
     \title Qutlook Example (ActiveQt)
+    \examplecategory {Desktop}
     \ingroup activeqt-examples
 
     \brief The Qutlook example demonstrates the use of ActiveQt to automate

examples/activeqt/simple/doc/src/simple.qdoc

@@ -49,6 +49,7 @@
 /*!
     \example activeqt/simple
     \title Simple Example (ActiveQt)
+    \examplecategory {Desktop}
     \ingroup activeqt-examples
 
     \brief The Simple example demonstrates the use

examples/activeqt/wrapper/doc/src/wrapper.qdoc

@@ -12,6 +12,7 @@
 /*!
     \example activeqt/wrapper
     \title Wrapper Example (ActiveQt)
+    \examplecategory {Desktop}
     \ingroup activeqt-examples
 
     \brief The Wrapper example demonstrates how to export existing QWidget