Editorial: fix #371 - better handling of completion values

[caridy]

cc @linusg

[linusg]

In case it is helpful, what I did in my implementation to work around the spec bug is simply Return result.:

https://github.com/SerenityOS/serenity/blob/dfb7588d300148ec72e1283947c4b37d71ffc460/Userland/Libraries/LibJS/Runtime/WrappedFunction.cpp#L75-L79

I was assuming that:

• Step 6 was supposed to handle normal completions, otherwise the [[Value]] from OrdinaryWrappedFunctionCall would be completely dropped in favor of returning undefined
• Step 7 would make step 8 redundant as only a normal or throw completion could be returned, and throw is handled by ReturnIfAbrupt

This implementation of ShadowRealm passes all 64 tests currently present in test262: https://libjs.dev/test262/per-file/?path=test/built-ins/ShadowRealm

So in case the desired behaviour is something else, that is currently not covered by tests (or unobservable).

[leobalter]

@rwaldron PTAL at the referred test262.