`details bind:open` should count as `[open]` for styling

[Conduitry]

<script>
	let open = false;
</script>

<details bind:open>Hello</details>

<style>
	details[open] {
		color: red;
	}
</style>

details[open] is getting removed because the compiler doesn't think that <details bind:open> indicates an open attribute that might be present.

[Conduitry]

I had assumed there was some precedent for handling this with other bindings, but thinking about it more, I'm not sure what bindings those would be. We might just need a weird one-off check for this when determining whether an element can match a selector.

[Conduitry]

diff --git a/src/compiler/compile/css/Selector.ts b/src/compiler/compile/css/Selector.ts
index ef54f789..e70b2986 100644
--- a/src/compiler/compile/css/Selector.ts
+++ b/src/compiler/compile/css/Selector.ts
@@ -219,6 +219,8 @@ function attribute_matches(node: Node, name: string, expected_value: string, ope
 	const spread = node.attributes.find(attr => attr.type === 'Spread');
 	if (spread) return true;
 
+	if (name === 'open' && node.bindings.some((binding: Node) => binding.name === 'open')) return true;
+
 	const attr = node.attributes.find((attr: Node) => attr.name === name);
 	if (!attr) return false;
 	if (attr.is_true) return operator === null;

This seems to do it. I don't know whether there is a more elegant way. It might make sense to always also search node.bindings, and if we find a binding, assume that it's always possible for this selector to match this element. I.e.:

diff --git a/src/compiler/compile/css/Selector.ts b/src/compiler/compile/css/Selector.ts
index ef54f789..0d4ea82b 100644
--- a/src/compiler/compile/css/Selector.ts
+++ b/src/compiler/compile/css/Selector.ts
@@ -219,6 +219,8 @@ function attribute_matches(node: Node, name: string, expected_value: string, ope
 	const spread = node.attributes.find(attr => attr.type === 'Spread');
 	if (spread) return true;
 
+	if (node.bindings.some((binding: Node) => binding.name === name)) return true;
+
 	const attr = node.attributes.find((attr: Node) => attr.name === name);
 	if (!attr) return false;
 	if (attr.is_true) return operator === null;