Move TextContent Java tests to C++ for ScEditFieldObj_Cell and
ScEditFieldObj_Header (formerly ScCellFieldObj).

Change-Id: Ieed5cdbc128490e66d1797c817d998a932317dd4
Reviewed-on: https://gerrit.libreoffice.org/70615
Tested-by: Jenkins
Reviewed-by: Jens Carl <j.carl43@gmx.de>