Auto merge of #75573 - Aaron1011:feature/const-mutation-lint, r=oli-obk

Add CONST_ITEM_MUTATION lint

Fixes #74053
Fixes #55721

This PR adds a new lint `CONST_ITEM_MUTATION`.
Given an item `const FOO: SomeType = ..`, this lint fires on:

* Attempting to write directly to a field (`FOO.field = some_val`) or
  array entry (`FOO.array_field[0] = val`)
* Taking a mutable reference to the `const` item (`&mut FOO`), including
  through an autoderef `FOO.some_mut_self_method()`

The lint message explains that since each use of a constant creates a
new temporary, the original `const` item will not be modified.

compiler/rustc_mir/src/transform/mod.rs

@@ -16,6 +16,7 @@ use std::borrow::Cow;
 pub mod add_call_guards;
 pub mod add_moves_for_packed_drops;
 pub mod add_retag;
+pub mod check_const_item_mutation;
 pub mod check_consts;
 pub mod check_packed_ref;
 pub mod check_unsafety;
@@ -307,6 +308,7 @@ fn mir_const<'tcx>(
         &[&[
             // MIR-level lints.
             &check_packed_ref::CheckPackedRef,
+            &check_const_item_mutation::CheckConstItemMutation,
             // What we need to do constant evaluation.
             &simplify::SimplifyCfg::new("initial"),
             &rustc_peek::SanityCheck,