message: Update mergeable type references after merging methods.
  Summary:
  Collect mergeable ctor callsite within the merger cls
  Update mergeable type reference after the method transformations
diff: @@ -379,7 +379,9 @@ void IRInstruction::normalize_registers() {
  ++old_srcs_idx;
  }
  for (size_t args_idx = 0; args_idx < args.size(); ++args_idx) {
  - always_assert(old_srcs_idx < srcs_size());
  + always_assert_log(old_srcs_idx < srcs_size(),
  + "Invalid arg indices in %s\n",
  + SHOW(this));
  set_src(srcs_idx++, src(old_srcs_idx));
  old_srcs_idx += is_wide_type(args.at(args_idx)) ? 2 : 1;
  }
  