Implement sass --embedded in pure JS mode

[ntkme]

Closes #2325.

sass/embedded-host-node#344

Implementation

The actual isolate dispatcher and compilation dispatcher are nearly unchanged. However, I had to replace isolate with worker communication, and mock tons of small things that do not work on node.

Testing

• All Dart embedded tests are passing. - GitHub CI has been updated to run these in this PR.
• All JS API tests are passing. - GitHub CI has been updated to run these in this PR.
• All Ruby API tests are passing.

[ntkme]

Applied most of the feedbacks. However, I have a awkward feeling about mixing classic js interop and new js interop in the same file, which is why I have lots of js specific things with new interop are only in embedded folder instead of in the generic folder.

@nex3 I haven't changed these yet, as I want to hear what's your thought on this.

[ntkme]

Another note: The reason I tried to avoid classic interop and node_introp is that I couldn't get channel.port2 passed to Worker() constructor correctly with node_interop. Neither allowInterop() nor explicit casting worked, and it was a nightmare trying to debug what went wrong. I looked at node_interop repo trying to see if there is any example for it and there is no actual usage of transferList anywhere.

The new dart 3.3 js interop on the other hands was way more straight forward to use and debug. I got Worker() working on my first attempt.