iitm wrappers copy exported primitives

[timfish]

When you export primitives in ESM, they are exposed as references which means they can be written to from elsewhere within the module. A reproduction of this behaviour can be seen in #113.

Because the iitm wrappers assign each export to a variable before re-exporting, primitive exports have their original value copied and the reference is lost.

This is where the code generation does that:

import-in-the-middle/hook.js

Lines 189 to 190 in 57d2459

	let $${n} = _.${n}
	export { $${n} as ${n} }

[timfish]

Ah, just realised this is a duplicate of #38