Auto merge of #98112 - saethlin:mir-alignment-checks, r=oli-obk

Insert alignment checks for pointer dereferences when debug assertions are enabled

Closes https://github.com/rust-lang/rust/issues/54915

- [x] Jake tells me this sounds like a place to use `MirPatch`, but I can't figure out how to insert a new basic block with a new terminator in the middle of an existing basic block, using `MirPatch`. (if nobody else backs up this point I'm checking this as "not actually a good idea" because the code looks pretty clean to me after rearranging it a bit)
- [x] Using `CastKind::PointerExposeAddress` is definitely wrong, we don't want to expose. Calling a function to get the pointer address seems quite excessive. ~I'll see if I can add a new `CastKind`.~ `CastKind::Transmute` to the rescue!
- [x] Implement a more helpful panic message like slice bounds checking.

r? `@oli-obk`

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -544,6 +544,12 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             RemainderByZero(op) => RemainderByZero(eval_to_int(op)?),
             ResumedAfterReturn(generator_kind) => ResumedAfterReturn(*generator_kind),
             ResumedAfterPanic(generator_kind) => ResumedAfterPanic(*generator_kind),
+            MisalignedPointerDereference { ref required, ref found } => {
+                MisalignedPointerDereference {
+                    required: eval_to_int(required)?,
+                    found: eval_to_int(found)?,
+                }
+            }
         };
         Err(ConstEvalErrKind::AssertFailure(err).into())
     }