Fix vp_get_interface_link_libraries CMake macro to support VTK 9.2.6

[fspindle]

…rings Qt6 when ustk is used as an external contrib module

When building ViSP with UsTK as a contrib module on macos

  UsTK 3rd parties:
    Use VTK:                     yes (ver 9.2.6)
    Use Qt:                      yes (ver 6)
    Use FFTW:                    yes
    Use Armadillo:               yes (ver 12.6.6)
    Use CUDA:                    no

vp_get_interface_link_libraries macro was unable to retrieve VTK link libraries, including things like $<..., >.
This PR fixes the macro.