Compilation fails if kernel name includes `!`

[AntonOresten]

It's not that important for kernels to allow ! since they are not user-facing and are inherently mutating, but I figured it's worth recording this since I was about to pull my hair out figuring out why an empty kernel was failing.😅

[maleadt]

We should allow all function names as Julia does, so let's keep this open.

[gbaraldi]

https://github.com/JuliaLang/julia/blob/1cba9c292c6bad490cca49cd52e333632a3fab91/src/aotcompile.cpp#L301-L325 is what we do to avoid issues like this

[maleadt]

I really hate the NOT suffixes though 😄