The body walker only visited `call` nodes, so a `fun Name/Arity`
reference — the idiomatic way to pass a local function to lists:map,
spawn, etc. — was dropped from the call graph. It parses as an
internal_fun node (name in the `fun` field, arity in the `arity` field).
Resolve it by exact name and arity and emit an indirect_call edge: the
function is handed off to be invoked, not called on the spot. Remote
references (fun mod:f/2, external_fun) name an explicit module and belong
to the cross-file remote-call boundary; they stay unresolved here.
Fixes#3993
(cherry picked from commit 1748e9bf0a)
rajatnagda45