Allow n_rows to be used inside aes()

[cararthompson]

I have been enjoying making waffles for a few projects - thanks for such a great package!

In the most recent one (see image), I was keen to try to balance things out by feeding n_rows into aes(), in order to have more rows on the top bar to balance things out a bit. I have no idea how difficult this would be to do, but thought it was worth asking.

Happy to provide a simple reprex if that would be helpful, but thought I'd first see if there was any interest in looking into this more.

Thanks!