Auto merge of #90218 - JakobDegen:adt_significant_drop_fix, r=nikomatsakis

Auto merge of #90218 - JakobDegen:adt_significant_drop_fix, r=nikomatsakis

Fixes incorrect handling of ADT's drop requirements

Fixes #90024 and a bunch of duplicates.

The main issue was just that the contract of `NeedsDropTypes::adt_components` was inconsistent; the list of types it might return were the generic parameters themselves or the fields of the ADT, depending on the nature of the drop impl. This meant that the caller could not determine whether a `.subst()` call was still needed on those types; it called `.subst()` in all cases, and this led to ICEs when the returned types were the generic params.

First contribution of more than a few lines, so feedback definitely appreciated.