ES modules with top-level await

Module mode lands with top-level await and a Test262 module runner; modules become runtime structures on the explicit frame stack like everything else.

5fba4d7d: "Run ES modules: top-level-await module mode + test262 module runner". The module graph, [[CycleRoot]], deferred evaluation ordering and errored-cycle re-import would each get their own fix over the following three months; today's zipp mjs is the descendant of this commit.