Bad code generated for self-referencing reactive value

[Rich-Harris]

REPL. This works for DOM code, as the let happens outside the update function:

<script>
	let number = 0;
	
	// this generates bad code in SSR mode
	$: max = Math.max(number, max || 0);
</script>

<style>
	input {
		width: 100%;
	}
</style>

<input type=range bind:value={number}>
<p>{number} / {max}</p>

In SSR mode, this code gets generated, resulting in a TDZ:

let max = Math.max(number, max || 0);

We could fix it straightforwardly enough by doing this instead:

let max; max = Math.max(number, max || 0);

Perhaps we should just do it in these rare cases though.