LibWeb/CSS: Move RuleContext type out of Parser.h

This was previously internal to the Parser, but we'd like to pass it in
from outside.

Libraries/LibWeb/CSS/Parser/RuleContext.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/FlyString.h>
+#include <LibWeb/CSS/CSSRule.h>
+
+namespace Web::CSS::Parser {
+
+enum class RuleContext : u8 {
+    Unknown,
+    Style,
+    AtMedia,
+    AtFontFace,
+    AtKeyframes,
+    Keyframe,
+    AtSupports,
+    SupportsCondition,
+    AtLayer,
+    AtProperty,
+};
+RuleContext rule_context_type_for_rule(CSSRule::Type);
+RuleContext rule_context_type_for_at_rule(FlyString const&);
+
+}