LibGfx+LibWeb: Store Typeface and Font-related types in RefPtr to const

Author: https://github.com/ADKaster
Commit: be2dd91289
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4362
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/Hendiadyoin1

Libraries/LibGfx/FontCascadeList.h

@@ -29,8 +29,8 @@ public:
             callback(font);
     }
 
-    void add(NonnullRefPtr<Font> font);
-    void add(NonnullRefPtr<Font> font, Vector<UnicodeRange> unicode_ranges);
+    void add(NonnullRefPtr<Font const> font);
+    void add(NonnullRefPtr<Font const> font, Vector<UnicodeRange> unicode_ranges);
 
     void extend(FontCascadeList const& other);
 
@@ -39,7 +39,7 @@ public:
     bool equals(FontCascadeList const& other) const;
 
     struct Entry {
-        NonnullRefPtr<Font> font;
+        NonnullRefPtr<Font const> font;
         Optional<Vector<UnicodeRange>> unicode_ranges;
     };