The return value of async function is not an instance of `Promise`

[R31K4G3]

When calling an async function, the returned value is expected to be a Promise.
However, p instanceof Promise is false in version 3.10.0 to 3.10.5.

const { VM } = require("vm2");

const vm = new VM();

const result = vm.run(`
async function f() {}

const p = f();

p instanceof Promise
`);

// Output: false
console.log(result);

[R31K4G3]

Why do both globalPromise (the original Promise class) and localPromise exist in lib/setup-sandbox.js?
localPromise is defined as class localPromise extends globalPromise {}, and that seems redundant.