project files: make GTestDir point to the submodule path
project files: make GTestDir point to the submodule path

- The GTestDir vsprop macro needs to point to the new google_test
  path now that it will be a submodule of npp-community super project.

Signed-off-by: Thell Fowler <46f1a0bd5592a2f9244ca321b129902a06b53e03@tbfowler.name>

npp-community/nppcr_googlemock,npp-community/nppcr_googlemock,npp-community/nppcr_googlemock