mergeAssets = (as1, as2) => {
	for (const [key, value1] of as2) {
		const value2 = as1.get(key);
		if (!value2 || value1 > value2) as1.set(key, value1);
	}
}
merge assets map 2 into map 1
@param {Assets} as1 assets
@param {Assets} as2 assets
@returns {void}