fix: Always use correct prototype for ordinary objects

[ExE-Boss]

Addresses part of https://github.com/GoogleChrome/proxy-polyfill/issues/14.

This makes it so that Proxies of ordinary objects are always created with target.[[Prototype]] as their prototype.

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[ExE-Boss]

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[samthor]

So I feel like, after some reading, is that this is really just adding improved older browser support. I can't find a practical way to test the outcomes in a modern browser (and I've not updated the tests to delete the things we're checking).

I have some tweaks I'll make afterwards but I'm happy.