src/vs/base/common/collections.ts/diffSets
export function diffSets<T>(before: Set<T>, after: Set<T>): { removed: T[]; added: T[] } {
	const removed: T[] = [];
	const added: T[] = [];
	for (let element of before) {
		if (!after.has(element)) {
			removed.push(element);
		}
	}
	for (let element of after) {
		if (!before.has(element)) {
			added.push(element);
		}
	}
	return { removed, added };
}