LibWeb/DOM: Add Document::in_limited_quirks_mode() helper

Author: https://github.com/AtkinsSJ
Commit: 7d502df807
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3168
Reviewed-by: https://github.com/gmta ✅

Libraries/LibWeb/DOM/Document.h

@@ -319,6 +319,7 @@ public:
 
     QuirksMode mode() const { return m_quirks_mode; }
     bool in_quirks_mode() const { return m_quirks_mode == QuirksMode::Yes; }
+    bool in_limited_quirks_mode() const { return m_quirks_mode == QuirksMode::Limited; }
     void set_quirks_mode(QuirksMode mode) { m_quirks_mode = mode; }
 
     Type document_type() const { return m_type; }