docs: private ImmutableList<SoyMsgPart> compactParts(ImmutableList<SoyMsgPart> parts) {
      ImmutableList.Builder<SoyMsgPart> builder = ImmutableList.builder();
      for (SoyMsgPart part : parts) {
        builder.add(compactPart(part));
      }
      return builder.build();
    }