Auto merge of rust-lang#128703 - compiler-errors:normalizing-tails, r=lcnr

Miscellaneous improvements to struct tail normalization

1. Make checks for foreign tails more accurate by normalizing the struct tail. I didn't write a test for this one.
2. Normalize when computing struct tail for `offset_of` for slice/str. This fixes the new solver only.
3. Normalizing when computing tails for disaligned reference check. This fixes both solvers.

r? lcnr

Author: bors

clippy_utils/src/qualify_min_const_fn.rs

@@ -142,7 +142,7 @@ fn check_rvalue<'tcx>(
                 // We cannot allow this for now.
                 return Err((span, "unsizing casts are only allowed for references right now".into()));
             };
-            let unsized_ty = tcx.struct_tail_erasing_lifetimes(pointee_ty, tcx.param_env(def_id));
+            let unsized_ty = tcx.struct_tail_for_codegen(pointee_ty, tcx.param_env(def_id));
             if let ty::Slice(_) | ty::Str = unsized_ty.kind() {
                 check_operand(tcx, op, span, body, msrv)?;
                 // Casting/coercing things to slices is fine.