3f58828fdc
Identify anonymous lifetimes by their DefId in HIR. `ParamName::Fresh` currently identifies anonymous lifetimes by an `usize` index computed from the number of lifetimes in scope. This makes the behaviour of lowering dependent on the contents of the surrounding item in unpredictable ways. This PR replaces this index by the `LocalDefId` of the synthetized generic lifetime parameter. This makes obvious which parameter the lifetime corresponds to.