Auto merge of #13950 - bheart:parse-font-language-override-property, r=emilio

Implement parsing for font-language-override property

Implement and test parsing of the `font-language-override` style property.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13874
- [x] There are tests for these changes

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tests/unit/style/parsing/font.rs

@@ -76,3 +76,31 @@ fn font_feature_settings_to_css() {
     assert_roundtrip_with_context!(font_feature_settings::parse, "\"abcd\" 4");
     assert_roundtrip_with_context!(font_feature_settings::parse, "\"abcd\", \"efgh\"");
 }
+
+#[test]
+fn font_language_override_should_parse_properly() {
+    use style::properties::longhands::font_language_override::{self, SpecifiedValue};
+
+    let normal = parse_longhand!(font_language_override, "normal");
+    assert_eq!(normal, SpecifiedValue::Normal);
+
+    let empty_str = parse_longhand!(font_language_override, "\"\"");
+    assert_eq!(empty_str, SpecifiedValue::Override("".to_string()));
+
+    let normal_str = parse_longhand!(font_language_override, "\"normal\"");
+    assert_eq!(normal_str, SpecifiedValue::Override("normal".to_string()));
+
+    let turkic = parse_longhand!(font_language_override, "\"TRK\"");
+    assert_eq!(turkic, SpecifiedValue::Override("TRK".to_string()));
+
+    let danish = parse_longhand!(font_language_override, "\"DAN\"");
+    assert_eq!(danish, SpecifiedValue::Override("DAN".to_string()));
+}
+
+#[test]
+#[should_panic]
+fn font_language_override_should_fail_on_empty_str() {
+    use style::properties::longhands::font_language_override::{self, SpecifiedValue};
+
+    parse_longhand!(font_language_override, "");
+}