Free (file-level) functions have been valid Solidity since 0.7, but the
extractor only descended into named type declarations (contract, library,
interface, abstract contract). A function declared at source-unit scope —
and every call made from its body — was dropped entirely, so a file of
free utility functions produced no nodes at all.
Walk source-unit function_definition nodes, emit each as a file-contained
callable node, and resolve an unambiguous same-file free-function call to a
calls edge. Member calls (Lib.f()) are parked as raw_calls for cross-file
resolution; calls that cross into contract scope are left unresolved rather
than guessed (fail-closed).
(cherry picked from commit d2e56e932f)
rajatnagda45