Function follow_shredded_path_element 

pub(crate) fn follow_shredded_path_element<'a>(
    shredding_state: &BorrowedShreddingState<'a>,
    path_element: &VariantPathElement<'_>,
    cast_options: &CastOptions<'_>,
) -> Result<ShreddedPathStep<'a>>

Given a shredded variant field – a (value?, typed_value?) pair – try to take one path step deeper. For a VariantPathElement::Field, the step fails if there is no typed_value at this level, or if typed_value is not a struct, or if the requested field name does not exist.

TODO: Support VariantPathElement::Index? It wouldn’t be easy, and maybe not even possible.