feat(internal): Support globalThis in modern environments

[warmrobot]

fix #3561

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Tests

• Run the tests tests with npm test or yarn test)

[arxpoetica]

Haven't actually tested, but scanning it looks right.

[Conduitry]

The code change itself does look good. The test failure looks to be probably an artifact of our test setup, and not an actual bug with the new code.

Favoring window over globalThis when selecting the globals object seems to make them all pass. I haven't yet gotten all the tests to pass when favoring globalThis, and I don't know whether that's going to end up being a worthwhile endeavor.

[warmrobot]

Tests passed on my mac, but failed on Parallels Ubuntu 18.04
It seems, that it failed to call scrollTo.

scrollTo$ is not a function

I try to debug test component this way:

import { beforeUpdate } from 'svelte'
	import  { globals } from '/home/parallels/Projects/svelte/internal'
	export let scrollY;

	beforeUpdate(() => {
		console.log('===================', globals.window.scrollTo, globals.scrollY, globals.pageYOffset)
	})

And results were:

=================== [Function] undefined undefined
=================== [Function] undefined undefined

Why globalThis important?
I think it is best approach when working in v8 environment (not Node). We already discussed this with you a few time ago.
Since then we have 2 new projects on Svelte on high load production. We've updated v8 to v8.0. So the last step is to support it in Svelte internals.

[Conduitry]

The test failure or success was presumably related to the version of Node (and whether it supported globalThis - using newer versions fails because using globalThis rather than window broke tests) and not the operating system. After spending a bit more time on this, I've just pushed a change to make it favor window over globalThis (which shouldn't have any effect in practice) so that the tests pass.

[warmrobot]

I checked it on v8 and it works perfectly. Now we can call Svelte truly 'environment agnostic'. Thank you! )