AMD loader only injected in entrypoint

[LarsDenBakker]

The AMD loader is only ever injected in the entry point due to this check: https://github.com/Polymer/tools/blob/master/packages/build/src/optimize-streams.ts#L223

This fails to account for situations where modules are loaded from a HTML import, but not the entrypoint.

I'm not sure if this can be fixed easily, as the current method is an easy way to ensure the loader is only injected once ever per project. An easy workaround is to add an empty module to the index.html, which will trigger the injection. A module correct way is to perhaps add a configuration option? Along with #495 a lot of the checks are es-module only oriented.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed after being marked stale. If you're still facing this problem with the above solution, please comment and we'll reopen!