Determine whether we need a node ID when resolving methods

[catamorphism]

See FIXME (formerly XXX) in the item_trait case in resolve::resolve_item.

[msullivan]

FIXME still there. We probably don't need a node_id, if it actually works...

[emberian]

/cc @pcwalton

[huonw]

Triage: FIXME is still there. I guess having a NodeId would make other tooling easier, e.g. #8961 would likely be easier to fix if every method had an associated NodeId (since it would then not require (as much) special casing).

[steveklabnik]

For future spelunkers, this is talking about

rust/src/librustc/middle/resolve.rs

Line 3724 in e2273d9

// FIXME #4951: Do we need a node ID here?