LibWeb: Parse oblique font-style with an angle value

Author: https://github.com/tcl3
Commit: c0f9b11070
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4552
Reviewed-by: https://github.com/konradekk

Libraries/LibWeb/CSS/CSSStyleValue.h

@@ -107,6 +107,7 @@ public:
         FitContent,
         Flex,
         FontSource,
+        FontStyle,
         FontVariant,
         Frequency,
         GridAutoFlow,
@@ -234,6 +235,10 @@ public:
     FontSourceStyleValue const& as_font_source() const;
     FontSourceStyleValue& as_font_source() { return const_cast<FontSourceStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_font_source()); }
 
+    bool is_font_style() const { return type() == Type::FontStyle; }
+    FontStyleStyleValue const& as_font_style() const;
+    FontStyleStyleValue& as_font_style() { return const_cast<FontStyleStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_font_style()); }
+
     bool is_frequency() const { return type() == Type::Frequency; }
     FrequencyStyleValue const& as_frequency() const;
     FrequencyStyleValue& as_frequency() { return const_cast<FrequencyStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_frequency()); }