Add `change_function_type` for HugrView DFGs

[lmondada]

SiblingSubgraph::create_simple_replacement as well as SimpleReplacement::try_new expect the type signature of the HUGR subgraph to match the type signature of the replacement DFG HUGR.

It would be useful to have a utility function that can reorder/copy/discard inputs and outputs of DFG graphs so that replacement graphs can be adjusted to match the subgraph signature.

Something like:

impl HugrView {
    /// Change the function type of a DFG HUGR by reordering/copying/discarding
    /// inputs and outputs of self.
    /// 
    /// Both `new_to_old_inputs` and `old_to_new_outputs` must be bijective when
    /// restricted to the set of linear values.
    fn change_function_type(
        &self,
        new_to_old_inputs: impl Fn(OutgoingPort) -> OutgoingPort,
        old_to_new_outputs: impl Fn(IncomingPort) -> IncomingPort,
    ) -> Hugr {
    }
}