Make sure to use Receiver trait when extracting object method candidate

[compiler-errors]

In method confirmation, the extract_existential_trait_ref function re-extracts the object type by derefing until it reaches an object. If we're assembling methods via the Receiver trait, make sure we re-do our work also using the receiver trait.

Fixes #135155

cc @adetaylor

[rustbot]

r? @Nadrieril

rustbot has assigned @Nadrieril.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[Nadrieril]

r? compiler