* Node buttons can now use the layout engine. a few simple
ones are converted. We'll keep this code in C for now,
python wouldn't help much here.
* For node buttons not using the layout engine, manually
computing the button height is not longer needed.
* Node inputs are still not RNA wrapped, would be good to
have these available as well for keying, but makesrna does
not have access to the bNodeTypes.
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