fix: Regression itemscope as boolean_attribute

[aMediocreDad]

Note Referenced Issue: #8413

Microdata

Microdata are a strange set of attributes which are ONLY defined in markup, and have no relationship to the underlying Document Object Model node. As such programmatically defining an element and setting a property on it with a given Microdata attribute will not work:
https://codepen.io/iambrosius/full/jOvXBBG

One can read more about microdata here: https://developer.mozilla.org/en-US/docs/Web/HTML/Microdata

The Problem

When an attribute is declared in the set of boolean_attributes:

svelte/src/shared/boolean_attributes.ts

Line 1 in aa4d0fc

const _boolean_attributes = [

And here:

svelte/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts

Line 340 in aa4d0fc

const attribute_lookup: { [key in BooleanAttributes]: AttributeMetadata } & { [key in string]: AttributeMetadata } = {

The generated code looks like this:

function create_fragment(ctx) {
	let div$;

	return {
		c() {
			div$ = element$("div");
			div$.itemscope = true; // <- This line!
		},
		m(target, anchor) {
			insert$(target, div$, anchor);
		},
		p: noop$,
		i: noop$,
		o: noop$,
		d(detaching) {
			if (detaching) detach$(div$);
		}
	};
}

The output above will not work as expected because, again, Microdata has no relationship to the underlying document node (it is strictly defined in markup).

This PR rewrites the itemscope test to be more accurate of what itemscope is intended to be, along with removing the declaration of itemscope as a boolean attribute in the respective files above.

In addition it adds a test for the hidden attribute which is an attribute actually tied to the equivalent dom node property.

I hope this helps prevent future regressions from happening

---

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Tests

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[aMediocreDad]

In the future, Microdata attributes should be handled in a similar fashion to xlink attributes. I would love to help with this, but uncertain of where to start.

[aMediocreDad]

Converted the itemscope test to a more general microdata test that should prevent regression in the setting of microdata attributes.

[dummdidumm]

Thank you!