Revamp Mandelbrot example: Revisit the documentaton

Remove "Example" from the title.

Edit the link (title) to the documentation of Mandelbrot in QThread
documentation.

Delete the foreach related sentence as we are trying to port away from
this Qt pseudo-keyword.

Task-number: QTBUG-108861
Pick-to: 6.6 6.5 6.6.0
Change-Id: I6d04f24ac9c1fa1efe30a947c2da2ec7475edc80
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

examples/corelib/threads/doc/src/mandelbrot.qdoc

@@ -3,7 +3,7 @@
 
 /*!
     \example threads/mandelbrot
-    \title Mandelbrot Example
+    \title Mandelbrot
     \ingroup qtconcurrent-mtexamples
 
     \brief The Mandelbrot example demonstrates multi-thread programming
@@ -151,7 +151,7 @@
     it needs to access \c{RenderThread}'s member variables (e.g., in
     \c render()).
 
-    The \c forever keyword is, like \c foreach, a Qt pseudo-keyword.
+    The \c forever keyword is a Qt pseudo-keyword.
 
     \snippet threads/mandelbrot/renderthread.cpp 4
     \snippet threads/mandelbrot/renderthread.cpp 5

src/corelib/thread/qthread.cpp

@@ -284,11 +284,11 @@ QThreadPrivate::~QThreadPrivate()
     If you don't call \l{QObject::setObjectName()}{setObjectName()},
     the name given to your thread will be the class name of the runtime
     type of your thread object (for example, \c "RenderThread" in the case of the
-    \l{Mandelbrot Example}, as that is the name of the QThread subclass).
+    \l{Mandelbrot} example, as that is the name of the QThread subclass).
     Note that this is currently not available with release builds on Windows.
 
     \sa {Thread Support in Qt}, QThreadStorage, {Synchronizing Threads},
-        {Mandelbrot Example}, {Semaphores Example}, {Wait Conditions Example}
+        Mandelbrot, {Semaphores Example}, {Wait Conditions Example}
 */
 
 /*!