Customize the native binary output file name

[carlosedp]

This allows customizing the output file name from out to anything.

Previously it would require:

  def nativeLink = T {
    os.Path(scalaNativeWorker().nativeLink(nativeConfig(), (T.dest / "binaryname").toIO))
  }

With this PR, it would be: def nativeBinaryName = "binaryname"

[carlosedp]

Now it's passing :)

[lefou]

Can you elaborate whether this is pure convenience or there is a real need for this? I'm not so deep in Scala Native workflows, so I also cc'ing @lolgab here.

[carlosedp]

It's purely for convenience for setting up the output binary name. Currently it's hard-coded to "out".

[carlosedp]

I changed to:

def nativeBinaryName: String = { this.toString }

So the output binary would be named as the object being generated (also could be set by the user if needed). I think it's even more useful and keeps build.sc cleaner.

[carlosedp]

I don't want to bloat the API in any way. The motivation is to give flexibility to the user without bloating build.sc itself (I remember as a user looking at both build.sc and build.sbt and thinking "why the hell are they so complex!"). No problem canceling this PR if it would cause maintenance burden in the future.