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

Enumerate lint expectations using AttrId

This PR implements the idea I outlined in https://github.com/rust-lang/rust/issues/127884#issuecomment-2240338547

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 https://github.com/rust-lang/rust/issues/127884

cc `@xFrednet`

tests/ui/lint/expect-unused-imports.rs

@@ -0,0 +1,9 @@
+//@ check-pass
+
+#![deny(unused_imports)]
+#![deny(unfulfilled_lint_expectations)]
+
+#[expect(unused_imports)]
+use std::{io, fs};
+
+fn main() {}

tests/ui/lint/rfc-2383-lint-reason/expect_warnings.rs

@@ -0,0 +1,6 @@
+//@ check-pass
+
+#![expect(warnings)]
+
+#[expect(unused)]
+fn main() {}

tests/ui/lint/rfc-2383-lint-reason/force_warn_expected_lints_fulfilled.stderr

@@ -1,3 +1,11 @@
+warning: denote infinite loops with `loop { ... }`
+  --> $DIR/force_warn_expected_lints_fulfilled.rs:8:5
+   |
+LL |     while true {
+   |     ^^^^^^^^^^ help: use `loop`
+   |
+   = note: requested on the command line with `--force-warn while-true`
+
 warning: unused variable: `x`
   --> $DIR/force_warn_expected_lints_fulfilled.rs:18:9
    |
@@ -28,13 +36,5 @@ warning: unused variable: `this_should_fulfill_the_expectation`
 LL |     let this_should_fulfill_the_expectation = "The `#[allow]` has no power here";
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_this_should_fulfill_the_expectation`
 
-warning: denote infinite loops with `loop { ... }`
-  --> $DIR/force_warn_expected_lints_fulfilled.rs:8:5
-   |
-LL |     while true {
-   |     ^^^^^^^^^^ help: use `loop`
-   |
-   = note: requested on the command line with `--force-warn while-true`
-
 warning: 5 warnings emitted