z_xxx_loan_mut functions are not defined for all types where they are necessary

[milyin]

Describe the release item

E.g. there is z_closure_reply_call function with prototype

pub extern "C" fn z_closure_reply_call(
    closure: &z_loaned_closure_reply_t,
    reply: &mut z_loaned_reply_t,
) 

but there is no z_reply_loan_mut function which can return &mut z_loaned_reply_t

This happens because z_xxx_loan_mut functions were introduced only if there are other functions accepting mutable loan reference. But as we can see, this is easy to forget to add z_xxx_loan_mut function when it's necessary.

The proposal is to just implement z_xxx_loan_mut for all types, near the corresponding z_xxx_loan ones.

Anyway these functions will make sense when z_take for mutable loaned references is implemented: eclipse-zenoh/zenoh#1372