doc: refactor C++ usage

The documentation mentions both a namespace that has been removed
and the use of the module include which should be avoided in user code.

This patch removes both, and adds CMake usage for the module.

Pick-to: 6.9 6.8
Change-Id: I378fbcaffa3edc5bdb94cdb7e05c9876b2418931
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

Author: sgaist

src/charts/doc/snippets/doc_src_qtcharts.cpp

@@ -1,12 +1,6 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
-//! [0]
-#include <QtCharts>
-
-using namespace QtCharts;
-//! [0]
-
 //! [1]
 qmake CONFIG+=static
 make

src/charts/doc/snippets/doc_src_qtcharts.pro

@@ -0,0 +1,15 @@
+// Copyright (C) 2025 Samuel Gaist <samuel.gaist@idiap.ch>
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+//! [cmakebuild]
+    \code
+    find_package(Qt6 COMPONENTS Charts REQUIRED)
+    target_link_libraries(mytarget PRIVATE Qt6::Charts)
+    \endcode
+//! [cmakebuild]
+
+//! [qmakebuild]
+    \code
+    QT += charts
+    \endcode
+//! [qmakebuild]

src/charts/doc/src/qtcharts-module-use.qdocinc

@@ -14,10 +14,8 @@
 
     \include deprecation-phase.qdocinc
 
-    If you intend to use Qt Charts C++ classes in your application, use the
-    following include and using directives:
-
-    \snippet doc_src_qtcharts.cpp 0
+    Using a Qt module's C++ API requires linking against the module library, either directly or through other dependencies.
+    Several build tools have dedicated support for this, including CMake and qmake.
 
     \if !defined(qtforpython)
     \note Projects created with Qt Creator's Qt Quick Application
@@ -26,9 +24,13 @@
     QApplication as the module depends on Qt's \l{Graphics View Framework}
     for rendering.
 
-    To link against the Qt Charts module, add this line to your \c qmake project file:
+    To use the module with CMake, use the \c{find_package()} command to locate
+    the needed module components in the \c{Qt6} package:
+    \include qtcharts-module-use.qdocinc cmakebuild
 
-    \snippet doc_src_qtcharts.pro 0
+    To use the module for building with qmake, add the module as a value of the
+    \c QT variable in the project's .pro file:
+    \include qtcharts-module-use.qdocinc qmakebuild
     \endif
 
     Each chart type is represented by the QAbstractSeries derived class. To create charts, the users have to use an instance of the related