QtConcurrent: fix examples of overloaded methods in docs

Wrap the overloaded methods in qOverload(), to make the examples
compile.

Also remove the extra whitespaces when declaring nested templates.

Change-Id: If438caa6d705d9036dae45278fb26e080918da89
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 8aefbe67bf445d51f41c16ec00bc5ce3ec18ded5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentfilter.cpp

@@ -121,7 +121,8 @@ QFuture<QImage> grayscaleImages = QtConcurrent::filtered(images, &QImage::isGray
 
 // create a set of all printable characters
 QList<QChar> characters = ...;
-QFuture<QSet<QChar> > set = QtConcurrent::filteredReduced(characters, &QChar::isPrint, &QSet<QChar>::insert);
+QFuture<QSet<QChar>> set = QtConcurrent::filteredReduced(characters, qOverload<>(&QChar::isPrint),
+                                                         qOverload<const QChar&>(&QSet<QChar>::insert));
 //! [7]
 
 
@@ -131,7 +132,8 @@ QFuture<QSet<QChar> > set = QtConcurrent::filteredReduced(characters, &QChar::is
 // create a dictionary of all lower cased strings
 extern bool allLowerCase(const QString &string);
 QStringList strings = ...;
-QFuture<QSet<int> > averageWordLength = QtConcurrent::filteredReduced(strings, allLowerCase, QSet<QString>::insert);
+QFuture<QSet<QString>> lowerCase = QtConcurrent::filteredReduced(strings, allLowerCase,
+                                                                 qOverload<const QString&>(&QSet<QString>::insert));
 
 // create a collage of all gray scale images
 extern void addToCollage(QImage &collage, const QImage &grayscaleImage);

src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentmap.cpp

@@ -135,7 +135,8 @@ QFuture<QImage> bgrImages = QtConcurrent::mapped(images,
 
 // Create a set of the lengths of all strings in a list.
 QStringList strings = ...;
-QFuture<QSet<int> > wordLengths = QtConcurrent::mappedReduced(strings, &QString::length, &QSet<int>::insert);
+QFuture<QSet<int>> wordLengths = QtConcurrent::mappedReduced(strings, &QString::length,
+                                                             qOverload<const int&>(&QSet<int>::insert));
 //! [8]
 
 
@@ -150,7 +151,8 @@ QFuture<int> averageWordLength = QtConcurrent::mappedReduced(strings, &QString::
 // Create a set of the color distribution of all images in a list.
 extern int colorDistribution(const QImage &string);
 QList<QImage> images = ...;
-QFuture<QSet<int> > totalColorDistribution = QtConcurrent::mappedReduced(images, colorDistribution, QSet<int>::insert);
+QFuture<QSet<int>> totalColorDistribution = QtConcurrent::mappedReduced(images, colorDistribution,
+                                                                        qOverload<const int&>(&QSet<int>::insert));
 //! [9]
 
 

src/concurrent/qtconcurrentfilter.cpp

@@ -134,7 +134,10 @@
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 7
 
-    Note that when using QtConcurrent::filteredReduced(), you can mix the use of
+    Note the use of qOverload. It is needed to resolve the ambiguity for the
+    methods, that have multiple overloads.
+
+    Also note that when using QtConcurrent::filteredReduced(), you can mix the use of
     normal and member functions freely:
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 8

src/concurrent/qtconcurrentmap.cpp

@@ -260,7 +260,10 @@
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 8
 
-    Note that when using QtConcurrent::mappedReduced(), you can mix the use of
+    Note the use of qOverload. It is needed to resolve the ambiguity for the
+    methods, that have multiple overloads.
+
+    Also note that when using QtConcurrent::mappedReduced(), you can mix the use of
     normal and member functions freely:
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 9