Using `dynamic_cast<AliasType>` to determine `pointee_depends_on_holder_owner`. (#2910)

* Adaption of PyCLIF virtual_py_cpp_mix test.

* Removing ValueError: Ownership of instance with virtual overrides in Python cannot be transferred to C++. TODO: static_assert alias class needs to inherit from virtual_overrider_self_life_support.

* Bringing back ValueError: "... instance cannot safely be transferred to C++.", but based on dynamic_cast<AliasType>.

* Fixing oversight: adding test_class_sh_virtual_py_cpp_mix.cpp to cmake file.

* clang <= 3.6 compatibility.

* Fixing oversight: dynamic_raw_ptr_cast_if_possible needs special handling for To = void. Adding corresponding missing test in test_class_sh_virtual_py_cpp_mix. Moving dynamic_raw_ptr_cast_if_possible to separate header.

* Changing py::detail::virtual_overrider_self_life_support to py::virtual_overrider_self_life_support.