Turn on module/no module support in Optimizer

Do not land till @kristoferbaxter gives go ahead that this has landed on cache

Let's move module/no module support in Optimizer from experimental to stable
Let's also confirm that iframes are also using esm version

cc @erwinmombay @caroqliu

No files, tests, or entry points are named. Start by locating the Optimizer's current experimental module/no-module handling and the iframe ESM path, then confirm with @kristoferbaxter that the cache work has landed. Done means the support is stable and iframe output uses the ESM version.

Written by the indexing model from the issue text.