[BUG] Rendering mismatch for the Grid's FilterRow cell

[NickIliev]

Bug report

The Grid's Filter Row is rendered with different CSS selectors compared to the source of truth tests. That results in ThemeBuilder producing styles incompatible with other Kendo/Telerik suites rendering for the filter row

Reproduction of the problem

• Load the basic KendoReact demo of the filter row from the documentation https://www.telerik.com/kendo-react-ui/components/grid/filtering/
• Add custom styles as generated from ThemeBuilder (Kendo Bootstrap theme)

Result: the styles for the component nested within the Filter Row are not properly applied The rendering shows the following structure:

The source of truth, however, is showing that there should be k-table-td class instead of the used k-table-th class. https://github.com/telerik/kendo-themes/blob/develop/tests/grid/grid-filter-row.html#L560

Environment

• Kendo UI version: Kendo React v8.0.0 reported through t.1654892

[silviyaboteva]

@ivanchev will take the PR into his while making the Grid a functional component.