gh-117953: Always Run Extension Init Func in Main Interpreter First (gh-118157)

gh-117953: Always Run Extension Init Func in Main Interpreter First (gh-118157)

This change makes sure all extension/builtin modules have their init function run first by the main interpreter before proceeding with import in the original interpreter (main or otherwise).  This means when the import of a single-phase init module fails in an isolated subinterpreter, it won't tie any global state/callbacks to the subinterpreter.