Fix the bindings for performance.now() and document.*

[CountBleck]

performance.now() and co. need to be called with the proper this value.

Changes proposed in this pull request:
⯈ Ensure performance.now() is called properly.
⯈ Ensure document.* is called properly.

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[CountBleck]

On a related note, does AS's document.cookie update throughout the page's lifetime?

[MaxGraey]

Hmm, it should be a default behavior until @external.js is not exposed explicitly. Perhaps better to fix this in src/bindings/js.ts

[CountBleck]

What about, say, importing functions from Wasm that return v128?
Anyhow, I think your idea should be as simple as removing this branch or adding a && isIdentifier(name) to the condition.

[CountBleck]

This PR should also fix #2692 (I hope).