Better error display in debugger panel

- Use the right stack frame info as title of the error.
- Use the actual C# exception type as error for exceptions raised from C#.
- Show the right language instead of always **C++ Error**.

editor/debugger/script_editor_debugger.h

@@ -210,6 +210,8 @@ private:
 
 	void _breakpoint_tree_clicked();
 
+	String _format_frame_text(const ScriptLanguage::StackInfo *info);
+
 protected:
 	void _notification(int p_what);
 	static void _bind_methods();