Using `--native` should automatically use (and install if needed) GraalVM

[quintesse]

Right now we simply expect GraalVM to be available, we don't do any checking if the current JDK is a GraalVM or if one could be installed. If we want --native to be really useful we should do this automatically.

This means that devkitman needs to support selecting and installing GraalVMs. (It can install them but right now it doesn't really know that there is a difference between "normal" JDKs and GraalVMs)

Edit: opened jbangdev/jbang-devkitman#64