Update Quick3d examples to use qt6_add_shaders()

In https://doc.qt.io/qt-6/qtshadertools-build.html

it is shown to use 
qt6_add_shaders()
to add custom shaders.

In current quick3d examples for example "Qt Quick 3d - Customer Shaders Example" the shaders have been added via qt_add_qml_module().

Should the examples be updated to use qt6_add_shaders() if it is the preferred way?