Fix binding this to a computed property

[btk5h]

This PR fixes #2333 by allowing flatten_reference to handle computed properties.

[btk5h]

Oops, this doesn't work with things like array indices of each blocks.

[Conduitry]

Thanks! I was just in the middle of writing up a comment saying that that's not working yet.

<script>
	import Foo from './Foo.svelte';
	let refs = [];
</script>

{#each { length: 5 } as _, i}
	<Foo bind:this={refs[i]}/>
{/each}

{JSON.stringify(refs)}

The foo_binding function looks like:

	function foo_binding($$component) {
		refs[i] = $$component;
		$$invalidate('refs', refs)
	}

I believe this function (and also where it's called) will need to be updated to use i as another argument. You can take a look at how this is implemented for DOM this bindings here.

[btk5h]

Should be fixed now!

[Conduitry]

Awesome, thank you so much!