Add github workflow job to build openmw on windows using vcpkg deps
https://github.com/elsid/openmw/actions/runs/9621169793 is the corresponding job on github. Produced binaries start successfully (no missing DLLs for openmw, cs, wizard, launcher). It does not use CI/before_script.msvc.sh
on purpose to show that it's possible to build openmw without it.