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.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/CSS/Parser/RuleContext.h>
+
+namespace Web::CSS::Parser {
+
+RuleContext rule_context_type_for_rule(CSSRule::Type rule_type)
+{
+    switch (rule_type) {
+    case CSSRule::Type::Style:
+        return RuleContext::Style;
+    case CSSRule::Type::Media:
+        return RuleContext::AtMedia;
+    case CSSRule::Type::FontFace:
+        return RuleContext::AtFontFace;
+    case CSSRule::Type::Keyframes:
+        return RuleContext::AtKeyframes;
+    case CSSRule::Type::Keyframe:
+        return RuleContext::Keyframe;
+    case CSSRule::Type::Supports:
+        return RuleContext::AtSupports;
+    case CSSRule::Type::LayerBlock:
+        return RuleContext::AtLayer;
+    case CSSRule::Type::NestedDeclarations:
+        return RuleContext::Style;
+    case CSSRule::Type::Property:
+        return RuleContext::AtProperty;
+        // Other types shouldn't be trying to create a context.
+    case CSSRule::Type::Import:
+    case CSSRule::Type::LayerStatement:
+    case CSSRule::Type::Namespace:
+        break;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+RuleContext rule_context_type_for_at_rule(FlyString const& name)
+{
+    if (name == "media")
+        return RuleContext::AtMedia;
+    if (name == "font-face")
+        return RuleContext::AtFontFace;
+    if (name == "keyframes")
+        return RuleContext::AtKeyframes;
+    if (name == "supports")
+        return RuleContext::AtSupports;
+    if (name == "layer")
+        return RuleContext::AtLayer;
+    if (name == "property")
+        return RuleContext::AtProperty;
+    return RuleContext::Unknown;
+}
+
+}