This adds zvfhmin test coverage for fceil, ffloor, fnearbyint, frint,
fround and froundeven and splits them at nxv32f16 to avoid crashing,
similarly to what we do for other nodes that we promote.
This also sets ftrunc to promote which was previously missing. We
already promote the VP version of it, vp_froundtozero.
Marking it as promoted affects some of the cost model tests since
they're no longer expanded.
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