[js-api] ToWebAssemblyValue signature change

[Ms2ger]

In #8, ToWebAssemblyValue gained an additional error argument; the current spec only passes it in a single call site. It seems like it had a caller that passed LinkError at the time. Presumably all callers should pass a value here; otherwise the argument should be marked as optional.

Alternatively, the algorithm should always throw a TypeError; that's what it already throws when ToInt32 and friends fail.

[ioannad]

I also think that the 3rd (error) argument of ToWebAssemblyValue can be safely removed, since there is no LinkError to propagate anymore. If such an error propagation is needed in the future, I would also go for an optional third argument.