Add `frunk` feature that derives `LabelledGeneric` for arrays to allow using `Transmogrifier` to select fields on generated array structs

[mbrobbel]

#[derive(frunk::labelled::LabelledGeneric)]
struct FooArray {
  a: BooleanArray,
  b: Uint32Array,
}

#[derive(frunk::labelled::LabelledGeneric)]
struct SelectA {
  a: BooleanArray,
}

let foo_array: FooArray = ...

// Select `a` from the FooArray
let select_a: SelectA = foo_array.transmogrify();

We could even generate these selector structs and add methods on the main array to use them.