LibGUI: Add formatter for ModelIndex.

Author: https://github.com/asynts
Commit: 93d04b9f8d
Pull-request: https://github.com/SerenityOS/serenity/pull/3696
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/emanuele6

Libraries/LibGUI/ModelIndex.cpp

@@ -47,3 +47,17 @@ const LogStream& operator<<(const LogStream& stream, const ModelIndex& value)
 }
 
 }
+
+namespace AK {
+
+void Formatter<GUI::ModelIndex>::format(TypeErasedFormatParams& params, FormatBuilder& builder, const GUI::ModelIndex& value)
+{
+    Formatter<StringView> formatter { *this };
+
+    if (value.internal_data())
+        formatter.format(params, builder, String::formatted("ModelIndex({},{},{:p})", value.row(), value.column(), value.internal_data()));
+    else
+        formatter.format(params, builder, String::formatted("ModelIndex({},{})", value.row(), value.column()));
+}
+
+}