message: fix shrinking cfg interaction
  Summary:
  The shrinker assumes that any incoming uneditable cfg is in good shape (for another round of constant-prop).
  However, FinalInlineV2 doesn't leave the cfg behind in a good shape.
  This is getting fixed here.
diff: @@ -946,6 +946,9 @@ size_t inline_final_gets(
  code.replace_opcode(p.first, p.second);
  }
  if (!replacements.empty() && maybe_shrinker) {
  + // We need to rebuild the cfg.
  + code.build_cfg(/* editable */);
  + code.clear_cfg();
  maybe_shrinker->shrink_method(method);
  }
  inlined_count.fetch_add(replacements.size());
  