Add support for ES `global` proposal

[mhegazy]

Here is the proposal: https://github.com/tc39/proposal-global

[DanielRosenwasser]

As discussed offline, it sounds like this is only a change to lib.d.ts, because anything else would be a polyfill.

[AaronNGray]

How about Global for the namespace ?

[saschanaz]

This has been fixed, you can use globalThis in the latest nightly build.

[DanielRosenwasser]

Fixed by #29332.