Getting/setting built-in methods should be rewritten or disallowed

[domenic]

Seen in #56.

const a = new Array();
const globalFunc = a.concat;

currently gets rewritten to

import Array, { concat_get as Array_concat_get } from "std:global/Array";
const a = new Array();
const globalFunc = Reflect_apply(Array_concat_get, a);

but should be rewritten to

import Array, { concat as Array_concat } from "std:global/Array";
const a = new Array();
const globalFunc = Array_concat;

The relevant criteria here is that the property concat is a function, and thus a method, not a getter/setter. I think we should basically special-case things that look like get/sets but whose type is Function.

(Technically it's possible to have a getter/setter that returns/accepts a function value, but I don't know of any instances of that across all the specs, and I doubt TypeScript has the type information to distinguish such cases. So, we'd probably need to handle them with a hard-coded list anyway, if such cases do exist.)

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Similar, but different: consider

const a = [];
a.concat = 5;

This should not be rewritten at all. This code (which is bad code) creates a data property on a; it does not try to set or override Array.prototype.concat. We should let it do that, I guess. Or, we could just disallow it; whichever is easier.