Upstreaming script type=module tests

[domenic]

WebKit and Edge have written a lot of web platform tests for script type=module. It'd be really great if we could get them upstreamed to web-platform-tests so that everyone benefits from everyone else's coverage.

• Edge tests: https://github.com/MicrosoftEdge/web-platform-tests/pull/18
• WebKit tests: WebKit/WebKit@750fa06

I think these should go under the category of "already reviewed upstream" so if their respective authors want to submit them as PRs to web-platform-tests, we should just rubber-stamp merge them immediately. Any review can be done as follow-up issues or PRs by reviewers. So for example we should not block merging these on Blink implementer review, but instead let Blink implementers try to pass them after they're already merged, and if Blink finds mistakes, Blink developers can send a follow-up PR.

/cc @rniwa, @AtOMiCNebula. Would you be willing to do the upstreaming?

[domenic]

Also worth noting is this test plan I put together which links out to individual WebKit and Edge tests that cover cases I thought of, plus contains a few items which I couldn't find tests for. https://docs.google.com/document/d/1ZfYUJG7tLvpJm1vleNfc5RoyoNx30NUNAOtnx_jhgRA/edit

[AtOMiCNebula]

It seems our MicrosoftEdge/web-platform-tests repo isn't being kept up to date with w3c's. Dang! I'll try to figure out what's going on over there, this should have been merged into w3c's shortly after I merged in to MicrosoftEdge's.

[AtOMiCNebula]

It sounds like we have some housekeeping issues going on in our clone. I rebased my change to get around a not-yet-upstreamed commit, see #4876.