message: Add comments explaining why we do something complex for (un)init
diff: @@ -331,6 +331,7 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for EvalContext<'a, 'mir, 'tcx, super:
  "likely" | "unlikely" | "forget" => {}
  "init" => {
  + // we don't want to force an allocation in case the destination is a simple value
  match dest {
  Place::Local { frame, local } => {
  match self.stack()[frame].locals[local].access()? {
  @@ -618,6 +619,7 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for EvalContext<'a, 'mir, 'tcx, super:
  }
  "uninit" => {
  + // we don't want to force an allocation in case the destination is a simple value
  match dest {
  Place::Local { frame, local } => {
  match self.stack()[frame].locals[local].access()? {
  