`fn compute_closure_requirements_modulo_opaques` shouldn't clone all its inputs

[lcnr]

#145925 added fn compute_closure_requirements_modulo_opaques which clones a bunch of borrowck state to be able to compute the propagated closure requirements for nested bodies without actually finishing borowck for it.

We should change the code to take at least some of the fields by reference/Rc instead of just cloning everything. See the relevant FIXME(#146079) in the source