Run UI tests in edition 2024 mode (#14602)

The `ui_test` package runs test in edition 2021 mode by default. This PR
switches our tests to edition 2024. The commits progressively make our
test suite compatible with both edition 2021 and edition 2024, then
switches the testing mode to edition 2024, which is compatible with what
`cargo dev lint` also uses by default.

The changes are (without functionality changes in tests):
- Add `unsafe` when [calling unsafe constructs inside `unsafe
fn`](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html),
to [unsafe
attributes](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-attributes.html),
and to [`extern`
blocks](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-extern.html).
- Use stricter reference patterns to accomodate with the [new match
ergonomics
rules](https://doc.rust-lang.org/edition-guide/rust-2024/match-ergonomics.html).
- Add some `use<>` markers where required to keep the same semantics
under the [new RPIT lifetime
rules](https://doc.rust-lang.org/edition-guide/rust-2024/rpit-lifetime-capture.html).

Some other changes ensure that non-regression tests are still enforced:
- Add edition 2021 specific tests when switching rules would make some
explicitly tested constructs untested, or when the test require using
the older [temporary tail expression scoping
rules](https://doc.rust-lang.org/edition-guide/rust-2024/temporary-tail-expr-scope.html).
- In `misnamed_getters`, check that getters containing an `unsafe` block
(for example a getter on an `Union` field) trigger the lint.

The last commit switches the default edition for running UI tests to
edition 2024.

changelog: [`misnamed_getters`]: getters containing an `unsafe` block
are also linted

clippy_lints/src/functions/misnamed_getters.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::source::snippet;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::FnKind;
-use rustc_hir::{Body, ExprKind, FnDecl, ImplicitSelfKind};
+use rustc_hir::{BlockCheckMode, Body, ExprKind, FnDecl, ImplicitSelfKind, UnsafeSource};
 use rustc_lint::LateContext;
 use rustc_middle::ty;
 use rustc_span::Span;
@@ -40,14 +40,25 @@ pub fn check_fn(cx: &LateContext<'_>, kind: FnKind<'_>, decl: &FnDecl<'_>, body:
         name
     };
 
-    // Body must be &(mut) <self_data>.name
+    // Body must be `&(mut) <self_data>.name`, potentially in an `unsafe` block
     // self_data is not necessarily self, to also lint sub-getters, etc…
 
     let block_expr = if let ExprKind::Block(block, _) = body.value.kind
         && block.stmts.is_empty()
         && let Some(block_expr) = block.expr
     {
-        block_expr
+        if let ExprKind::Block(unsafe_block, _) = block_expr.kind
+            && unsafe_block.stmts.is_empty()
+            && matches!(
+                unsafe_block.rules,
+                BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
+            )
+            && let Some(unsafe_block_expr) = unsafe_block.expr
+        {
+            unsafe_block_expr
+        } else {
+            block_expr
+        }
     } else {
         return;
     };