Rollup merge of #123487 - rcvalle:rust-cfi-restore-typeid-for-instance, r=compiler-errors

CFI: Restore typeid_for_instance default behavior

Restore typeid_for_instance default behavior of performing self type erasure, since it's the most common case and what it does most of the time. Using concrete self (or not performing self type erasure) is for assigning a secondary type id, and secondary type ids are only assigned when they're unique and to methods, and also are only tested for when methods are used as function pointers.

Author: GuillaumeGomez