QtCharts seem to have additional layer that prevents promotion on Designer

QPieSeries resides in `PySide2.QtCharts.QtCharts.QPieSeries`. This apparently causes trouble with Designer promotion system.

When I set class name as `QPieSeries` and header as `PySide2.QtCharts.QtCharts`, python complains `ModuleNotFoundError: No module named 'PySide2.QtCharts.QtCharts'; 'PySide2.QtCharts' is not a package`

When I set class name as `QtCharts.QPieSeries` and header as `PySide2.QtCharts`, python complains `from PySide2.QtCharts import QtCharts.QPieSeries` is an invalid syntax (the second dot)

Importing `from PySide2.QtCharts import *`, and then using `QtCharts.QPieSeries` seems to work, but it doesn't seem to be the right way to use in conjunction with Designer / PySide UIC.

Related issue: https://bugreports.qt.io/browse/PYSIDE-1173

For comparison, PyQt5 structures it like `PyQt5.QtChart.QPieSeries` (Note lack of the plurality on the package name)

(Issue filed with the help of fine person named "altendky" on IRC)