VS: Fix Fortran target type selection when linking C++ targets
Since !643 (merged) we consider the linker language when detecting whether to generate a
.vcxproj file. However, this could cause C-only projects to become
.vfproj files if they link to Fortran projects. Instead we should consider only the
LINKER_LANGUAGE property on the target itself. This approach is already used for CSharp. It allows project code to specify the project file type for a target with no sources but does not allow linked targets to affect it.
Fixes: #18687 (closed)