Provide standalone ParseScript wrapper

[annevk]

For use by whatwg/fetch#1442.

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Writing this up made me consider again whether we can pull in some of the encoding aspects as previously discussed, but I couldn't find a way that works well for all callers of "create a classic script". The main benefit of taking this PR would be that if JavaScript ever changes how this works, we only have to update HTML. Although if the return type changes I suppose we still need to update Fetch...

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/webappapis.html ( diff )

[domenic]

Hmm, I think having Fetch call ParseScript directly seems better. Although I understand the instinct, the part where you basically have an optional argument that takes you down the HTML-path or the Fetch-path makes this feel like not a very worthwhile wrapper.

[annevk]

That's fine too. My PR currently invokes ParseText directly, but I suppose if passing undefined and empty as second and third arguments is reasonable perhaps ParseScript is slightly better so I don't have to take a dependency on goal symbols.

@bakkot @ljharb thoughts?

[domenic]

IMO it's kind of undesired to pass undefined for the realm argument to ParseScript, even though technically it is just a pass-through. So that's why I like ParseText.

[bakkot]

ParseScript just invokes ParseText(x, |Script|) and wraps up a couple values into a record, so if you don't want the "construct a record" part it makes more sense invoke ParseText directly, IMO.

[annevk]

Thanks!