normalize better

[lukas-code]

// u*, i*, f*, bool, char, !, arrays, references, pointers, fn pointers,
// fn items, dyn* (dyn-star), closures, coroutines, enums, unions
impl Pointee for {trivially_sized} {
    default type Metadata = ();
}

impl Pointee for {extern_type} {
    default type Metadata = ();
}

impl Pointee for [{ty}] {
    default type Metadata = usize;
}

impl Pointee for str {
    default type Metadata = usize;
}

impl Pointee for dyn {predicates} + '{lifetime} {
    default type Metadata = DynMetadata<dyn {predicates} + '{lifetime}>;
}

// any struct without fields, including `PhantomData`
impl Pointee for {unit_struct} {
    default type Metadata = ();
}

// project to the last field of the struct
impl Pointee for {non_unit_struct} {
    default type Metadata = <{shallow_struct_tail} as Pointee>::Metadata;
}

// this specialization takes priority of all other impls for sized types
impl<T> Pointee for T {
    type Metadata = ();
}