Rollup merge of #140794 - karolzwolak:allow-unused-doc-65464, r=davidtwco

mention lint group in default level lint note

### Summary

This PR updates lint diagnostics so that default-level notes now mention the lint group they belong to, if any.
Fixes: rust-lang/rust#65464.

### Example

```rust
fn main() {
    let x = 5;
}
```

Before:

```
= note: `#[warn(unused_variables)]` on by default
```

After:

```
= note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default
```

### Unchanged Cases

Messages remain the same when the lint level is explicitly set, e.g.:

* Attribute on the lint `#[warn(unused_variables)]`:

  ```
  note: the lint level is defined here
  LL | #[warn(unused_variables)]
     |        ^^^^^^^^^^^^^^^^
  ```
* Attribute on the group `#[warn(unused)]:`:

  ```
  = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
  ```
* CLI option `-W unused`:

  ```
  = note: `-W unused-variables` implied by `-W unused`
  = help: to override `-W unused` add `#[allow(unused_variables)]`
  ```
* CLI option `-W unused-variables`:

  ```
  = note: requested on the command line with `-W unused-variables`
  ```

1 files changed, 8 insertions, 2 deletions

diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index cb159a0b914..e9bd9dccdf1 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -24,7 +24,7 @@ use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::print::{PrintError, PrintTraitRefExt as _, Printer, with_no_trimmed_paths};
 use rustc_middle::ty::{self, GenericArg, RegisteredTools, Ty, TyCtxt, TypingEnv, TypingMode};
 use rustc_session::lint::{FutureIncompatibleInfo, Lint, LintBuffer, LintExpectationId, LintId};
-use rustc_session::{LintStoreMarker, Session};
+use rustc_session::{DynLintStore, Session};
 use rustc_span::edit_distance::find_best_match_for_names;
 use rustc_span::{Ident, Span, Symbol, sym};
 use tracing::debug;
@@ -62,7 +62,13 @@ pub struct LintStore {
     lint_groups: FxIndexMap<&'static str, LintGroup>,
 }
 
-impl LintStoreMarker for LintStore {}
+impl DynLintStore for LintStore {
+    fn lint_groups_iter(&self) -> Box<dyn Iterator<Item = rustc_session::LintGroup> + '_> {
+        Box::new(self.get_lint_groups().map(|(name, lints, is_externally_loaded)| {
+            rustc_session::LintGroup { name, lints, is_externally_loaded }
+        }))
+    }
+}
 
 /// The target of the `by_name` map, which accounts for renaming/deprecation.
 #[derive(Debug)]