Set style attribute correctly when spread attr present

[kaisermann]

Related to #1664

[jacwright]

Adding a runtime test for this would be a great addition.

[kaisermann]

@jacwright I agree. I just don't know how to check specifically for the style.cssText since jsdom accepts assigning css directly to the style prop.

The test

<div {...props}>red text</div>

<script>
	export default {
		data: () => ({
			props: {
				style: 'color: red;'
			}
		})
	};
</script>

would pass without this PR but would fail in some older browsers 🤔

[jacwright]

Ah, I see. 👍

[Rich-Harris]

thank you!