[flang] Use fir.rebox for tbp fir.dispatch call with allocatable or pointer

Polymorphic entities with allocatable or pointer attribute cannot be passed
directly as passed-object when the type-bound procedure is expecting a
simply dummy polymorphic entity. Use fir.rebox to adapt the fir.class box
to the tbp type.

Depends on D135649

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D135654