refactor: Use ProxyCreate to remove setTimeout

[ExE-Boss]

Since #67 made it so that the value of this is irrelevant after the newTarget check, this moves the proxy construction into a ProxyCreate helper function, which is based on the ProxyCreate abstract operation, but takes an additional allowRevocation parameter, which is used to conditionally create the revoke function only when necessary, which also follows the spec more closely.

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It also fixes the issue listed in:

proxy-polyfill/src/proxy.js

Lines 86 to 88 in 60b4e5e

	// Construct revoke function, and set lastRevokeFn so that Proxy.revocable can steal it.
	// The caller might get the wrong revoke function if a user replaces or wraps scope.Proxy
	// to call itself, but that seems unlikely especially when using the polyfill.

[samthor]

Thanks, this is much nicer.