Auto merge of #130050 - cjgillot:expect-attr-id, r=fee1-dead

Enumerate lint expectations using AttrId

This PR implements the idea I outlined in rust-lang/rust#127884 (comment)

We can uniquely identify a lint expectation `#[expect(lint0, lint1...)]` using the `AttrId` and the index of the lint inside the attribute. This PR uses this property in `check_expectations`.

In addition, this PR stops stashing expected diagnostics to wait for the unstable -> stable `LintExpectationId` mapping: if the lint is emitted with an unstable attribute, it must have been emitted by an `eval_always` query (like inside the resolver), so won't be loaded from cache. Decoding an `AttrId` from the on-disk cache ICEs, so we have no risk of accidentally checking an expectation.

Fixes rust-lang/rust#127884

cc `@xFrednet`

Author: bors