TypeScript cells do not handle imports correctly

[mbostock]

It appears that the TypeScript transpiler is implicitly stripping unused imports (even though they are in fact “used” because the code will be rewritten to expose the imported symbols as top-level variables). Also, by default it appears to generate a CommonJS module, or something. So this:

import {foo} from "npm:bar";

Is being converted into this:

export {};

When it shouldn’t be changed at all. I suspect we are passing the wrong arguments to transpile.