Add Engine.print_error_messages property to disable printing errors

This can be used during unit test suite runs to hide error and warning
messages.

Care should be taken when using this feature, as it can hide important
information if used wrongly.

core/core_bind.h

@@ -660,6 +660,9 @@ public:
 	void set_editor_hint(bool p_enabled);
 	bool is_editor_hint() const;
 
+	void set_print_error_messages(bool p_enabled);
+	bool is_printing_error_messages() const;
+
 	_Engine() { singleton = this; }
 };