LibWeb/CSS: Parse the tab-size property

Author: https://github.com/kostyafarber
Commit: 68a28ff33a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1560
Reviewed-by: https://github.com/AtkinsSJ ✅

Userland/Libraries/LibWeb/CSS/StyleProperties.h

@@ -113,6 +113,7 @@ public:
     ContentDataAndQuoteNestingLevel content(DOM::Element&, u32 initial_quote_nesting_level) const;
     Optional<CSS::ContentVisibility> content_visibility() const;
     Optional<CSS::Cursor> cursor() const;
+    Variant<LengthOrCalculated, NumberOrCalculated> tab_size() const;
     Optional<CSS::WhiteSpace> white_space() const;
     Optional<CSS::LineStyle> line_style(CSS::PropertyID) const;
     Optional<CSS::OutlineStyle> outline_style() const;