Module Worker support

[rektide]

• https://html.spec.whatwg.org/multipage/workers.html#module-worker-example
• https://bugs.chromium.org/p/chromium/issues/detail?id=680046

#3877 depends on this feature.

[Malvoz]

+1

[TRayT]

+1

[SnirBroshi]

+1