AK+Everywhere: Change int to size_t in JsonObject and JsonArray

Author: https://github.com/MaxWipfli
Commit: f45273649f
Pull-request: https://github.com/SerenityOS/serenity/pull/8293
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/awesomekling

AK/JsonObject.h

@@ -44,7 +44,7 @@ public:
         return *this;
     }
 
-    int size() const { return m_members.size(); }
+    size_t size() const { return m_members.size(); }
     bool is_empty() const { return m_members.is_empty(); }
 
     JsonValue const& get(String const& key) const