Meta/CodeGenerators+LibWeb: Add support for 'easing-function' CSS values

This commit makes it possible to let properties accept easing functions
as values, which will be used in a later commit to implement
animation-timing-function.

Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateCSSPropertyID.cpp

@@ -20,7 +20,10 @@ ErrorOr<void> generate_bounds_checking_function(JsonObject& properties, SourceGe
 
 static bool type_name_is_enum(StringView type_name)
 {
-    return !AK::first_is_one_of(type_name, "angle"sv, "color"sv, "custom-ident"sv, "frequency"sv, "image"sv, "integer"sv, "length"sv, "number"sv, "paint"sv, "percentage"sv, "ratio"sv, "rect"sv, "resolution"sv, "string"sv, "time"sv, "url"sv);
+    return !AK::first_is_one_of(type_name,
+        "angle"sv, "color"sv, "custom-ident"sv, "easing-function"sv, "frequency"sv, "image"sv,
+        "integer"sv, "length"sv, "number"sv, "paint"sv, "percentage"sv, "ratio"sv, "rect"sv,
+        "resolution"sv, "string"sv, "time"sv, "url"sv);
 }
 
 ErrorOr<int> serenity_main(Main::Arguments arguments)
@@ -158,6 +161,7 @@ enum class ValueType {
     Angle,
     Color,
     CustomIdent,
+    EasingFunction,
     FilterValueList,
     Frequency,
     Image,
@@ -614,6 +618,8 @@ bool property_accepts_type(PropertyID property_id, ValueType value_type)
                     TRY(property_generator.try_appendln("        case ValueType::Color:"));
                 } else if (type_name == "custom-ident") {
                     TRY(property_generator.try_appendln("        case ValueType::CustomIdent:"));
+                } else if (type_name == "easing-function") {
+                    TRY(property_generator.try_appendln("        case ValueType::EasingFunction:"));
                 } else if (type_name == "frequency") {
                     TRY(property_generator.try_appendln("        case ValueType::Frequency:"));
                 } else if (type_name == "image") {

Userland/Libraries/LibWeb/CSS/CSSNumericType.cpp

@@ -33,6 +33,7 @@ Optional<CSSNumericType::BaseType> CSSNumericType::base_type_from_value_type(Val
 
     case ValueType::Color:
     case ValueType::CustomIdent:
+    case ValueType::EasingFunction:
     case ValueType::FilterValueList:
     case ValueType::Image:
     case ValueType::Integer:

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -8329,6 +8329,11 @@ ErrorOr<Parser::PropertyAndValue> Parser::parse_css_value_for_properties(Readonl
 
     auto& peek_token = tokens.peek_token();
 
+    if (auto property = any_property_accepts_type(property_ids, ValueType::EasingFunction); property.has_value()) {
+        if (auto maybe_easing_function = TRY(parse_easing_value(tokens)))
+            return PropertyAndValue { *property, maybe_easing_function };
+    }
+
     if (peek_token.is(Token::Type::Ident)) {
         // NOTE: We do not try to parse "CSS-wide keywords" here. https://www.w3.org/TR/css-values-4/#common-keywords
         //       These are only valid on their own, and so should be parsed directly in `parse_css_value()`.