Fix Java depfile error with Visual Studio generator

The DEPFILE files for the .java custom command were being written
to vtk<Module>Java.dir/<Class>.java.d, which caused errors on the
Visual Studio generators because the vtk<Module>Java.dir folders
only exist for Ninja and Makefile generators.  This is fixed by
writing the DEPFILE to vtk<Module>Java/<Class>.java.d instead.