LibWeb/MathML: Parse mathcolor and mathbackground as <color>

The difference is that parsing as the `color` property's value also
allows the CSS-wide keywords, which we don't want here.

The added test cases make sure that those keywords are *not* valid:
- `color` should inherit its parent value of `orange`
- `background-color` doesn't inherit, so should be its initial value of
  `transparent`

Libraries/LibWeb/MathML/MathMLElement.cpp

@@ -91,10 +91,10 @@ void MathMLElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties>
             // The mathcolor and mathbackground attributes, if present, must have a value that is a <color>. In that case,
             // the user agent is expected to treat these attributes as a presentational hint setting the element's color
             // and background-color properties to the corresponding values.
-            if (auto parsed_value = parse_css_value(CSS::Parser::ParsingParams { document() }, value, CSS::PropertyID::Color))
+            if (auto parsed_value = parse_css_type(CSS::Parser::ParsingParams { document() }, value, CSS::ValueType::Color))
                 cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::Color, parsed_value.release_nonnull());
         } else if (name == AttributeNames::mathbackground) {
-            if (auto parsed_value = parse_css_value(CSS::Parser::ParsingParams { document() }, value, CSS::PropertyID::BackgroundColor))
+            if (auto parsed_value = parse_css_type(CSS::Parser::ParsingParams { document() }, value, CSS::ValueType::Color))
                 cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::BackgroundColor, parsed_value.release_nonnull());
         } else if (name == AttributeNames::mathsize) {
             // https://w3c.github.io/mathml-core/#dfn-mathsize

Tests/LibWeb/Text/expected/MathML/presentational_hints.txt

@@ -3,8 +3,10 @@ direction: ltr
 direction: rtl
 color: red
 color: rgb(255, 0, 0)
+color: orange
 background-color: blue
 background-color: rgb(0, 0, 255)
+background-color: transparent
 font-size: 10px
 font-size: 24px
 font-size: 32px

Tests/LibWeb/Text/input/MathML/presentational_hints.html

@@ -7,13 +7,15 @@
         <mi dir="LTR"></mi>
         <mi dir="rtl"></mi>
     </math>
-    <math data-prop="color">
+    <math data-prop="color" style="color: orange">
         <mi mathcolor="red"></mi>
         <mi mathcolor="#f00"></mi>
+        <mi mathcolor="initial"></mi>
     </math>
-    <math data-prop="background-color">
+    <math data-prop="background-color" style="background-color: orange">
         <mi mathbackground="blue"></mi>
         <mi mathbackground="#0000ff"></mi>
+        <mi mathbackground="inherit"></mi>
     </math>
     <math data-prop="font-size">
         <mi mathsize="10px"></mi>