[`filter_map_bool_then`]: include multiple derefs from adjustments
In #11506 this lint was improved to suggest one deref if the bool is behind references (fixed the FP #11503), however it might need multiple dereferences if the bool is behind multiple layers of references or custom derefs. E.g. `&&&bool` needs `***b`.
changelog: [`filter_map_bool_then`]: suggest as many dereferences as there are needed to get to the bool