Update QtConcurrent docs and examples for reductor object usage

After 6ebe3d0f08 users don't have to
specify the result type when using functors for as a reductor.

Task-number: QTBUG-88448
Change-Id: I065fed11c1a66833ba0aac3d18e7ff0545247be1
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

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

@@ -177,9 +177,7 @@ struct StringTransform
 };
 
 QFuture<QString> fooString =
-  QtConcurrent::filteredReduced<QString>(strings,
-                                         StartsWith(QLatin1String("Foo")),
-                                         StringTransform());
+        QtConcurrent::filteredReduced(strings, StartsWith(QLatin1String("Foo")), StringTransform());
 //! [14]
 
 //! [15]
@@ -196,7 +194,7 @@ QList<int> results = future.results();
 
 // add up all even integers
 QList<int> list3 { 1, 2, 3, 4 };
-int sum = QtConcurrent::filteredReduced<int>(list3,
+QFuture<int> sum = QtConcurrent::filteredReduced(list3,
     [](int x) {
         return (x & 1) == 0;
     },
@@ -213,7 +211,7 @@ void intSumReduce(int &sum, int x)
 }
 
 QList<int> list { 1, 2, 3, 4 };
-int sum = QtConcurrent::filteredReduced(list,
+QFuture<int> sum = QtConcurrent::filteredReduced(list,
     [] (int x) {
         return (x & 1) == 0;
     },
@@ -228,7 +226,7 @@ bool keepEvenIntegers(int x)
 }
 
 QList<int> list { 1, 2, 3, 4 };
-int sum = QtConcurrent::filteredReduced<int>(list,
+QFuture<int> sum = QtConcurrent::filteredReduced(list,
     keepEvenIntegers,
     [](int &sum, int x) {
         sum += x;

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

@@ -165,10 +165,8 @@ struct ImageTransform
 };
 
 QFuture<QImage> thumbNails =
-  QtConcurrent::mappedReduced<QImage>(images,
-                                      Scaled(100),
-                                      ImageTransform(),
-                                      QtConcurrent::SequentialReduce);
+        QtConcurrent::mappedReduced(images, Scaled(100), ImageTransform(),
+                                    QtConcurrent::SequentialReduce);
 //! [11]
 
 //! [13]
@@ -223,7 +221,7 @@ QList<QImage> collage = QtConcurrent::mappedReduced(images,
 //! [16]
 
 //! [17]
-QList<QImage> collage = QtConcurrent::mappedReduced<QImage>(images,
+QList<QImage> collage = QtConcurrent::mappedReduced(images,
         [&size](const QImage &image) {
             return image.scaled(size, size);
         },

src/concurrent/qtconcurrentfilter.cpp

@@ -148,9 +148,7 @@
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 13
 
-    For the reduce function, function objects are not directly
-    supported. Function objects can, however, be used
-    when the type of the reduction result is explicitly specified:
+    Function objects are also supported for the reduce function:
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 14
 
@@ -168,9 +166,7 @@
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 16
 
-    For the reduce function, lambda expressions are not directly supported.
-    Lambda expressions can, however, be used when the type of the reduction
-    result is explicitly specified:
+    You can also pass a lambda as a reduce object:
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 17
 

src/concurrent/qtconcurrentmap.cpp

@@ -274,9 +274,7 @@
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 14
 
-    For the reduce function, function objects are not directly
-    supported. Function objects can, however, be used
-    when the type of the reduction result is explicitly specified:
+    Function objects are also supported for the reduce function:
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 11
 
@@ -294,9 +292,7 @@
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 16
 
-    For the reduce function, lambda expressions are not directly supported.
-    Lambda expressions can, however, be used when the type of the reduction
-    result is explicitly specified:
+    You can also pass a lambda as a reduce object:
 
     \snippet code/src_concurrent_qtconcurrentmap.cpp 17