Document partNameGenerator and make changes with classNameGenerator issue

[fractal3000]

Information about partNameGenerator is absend in our documentation(link below) so it shoud be added to the page https://docs.jmix.io/jmix/2.2/flow-ui/vc/components/dataGrid.html But information about classNameGenerator should be brought into line(deleted or corrected) with changes of the issue https://github.com/jmix-framework/jmix/issues/3515