fix: [#1855] Add Symbol.iterator to CSSStyleDeclaration for iteration support

[TrevorBurnham]

Fixes #1855

The CSSStyleDeclaration class was missing the Symbol.iterator implementation, which prevented users from iterating over style properties using for...of loops, the spread operator, or Array.from().

Changes

• Added [Symbol.iterator]() generator method to CSSStyleDeclaration class
• Added tests for iteration functionality

Before

const myElement = document.createElement('div');
myElement.setAttribute('style', 'background:red');

for (const key of myElement.style) {
  console.log(key);
}
// TypeError: myElement.style is not iterable

After

const myElement = document.createElement('div');
myElement.setAttribute('style', 'background:red');

for (const key of myElement.style) {
  console.log(key);
}
// Outputs: background-image, background-position-x, background-position-y, etc.

// Also works with spread operator
console.log([...myElement.style]);

// And Array.from()
console.log(Array.from(myElement.style));

[capricorn86]

Thank you for your contribution @TrevorBurnham! ⭐

I believe that the implementation can be done in a more efficient way (see comment).

[capricorn86]

Suggested change

	const length = propertyManager.size();
	for (let i = 0; i < length; i++) {
	yield propertyManager.item(i);
	}
	return Object.keys(propertyManager.properties)[Symbol.iterator]]();

I believe that this is more performant.

[TrevorBurnham]

Good catch! I've updated this PR to use a more performant approach for this iteration.

[TrevorBurnham]

CI failure appears to be due to #2022, which has a patch pending: #2023.