QtDataVisualization is namespaced

QtDataVisualization still has a dedicated namespace. QtCharts has already removed theirs
"Remove charts namespace for Qt6" 227020b118fa38ada1d8bd579593dae61f6e3881 https://codereview.qt-project.org/c/qt/qtcharts/+/308900 .

. Having the namespace results in annoying double namespacing in PySide such as <class 'PySide2.QtDataVisualization.QtDataVisualization.Q3DBars'>.

In the case of any widgets, this makes it impossible to setup promotion in Designer to widgets in the namespace. Though the promotion bit may not apply to data visualization as it doesn't seem to have widgets.

Are there any other modules with dedicated namespaces that should get cleaned up?

This follows from PYSIDE-1474.