proot-of-concept trace rework

[nadako]

I've accidentally stumbled upon one of my old branches and found it interesting :)

This is a proof-of-concept of how trace could be handled in a less hacky and more versatile way:

Instead of hard-coding trace and everything about it into the typer (and `trace as well), we provide a global static import from haxe.Trace.trace, where haxe.Trace is an extern class with the static trace method that takes Rest arguments.

Then, at the filters stage we rewrite calls to it into haxe.Log.trace calls so it behaves the same. But the cool part is that the user can provide their own haxe.Trace with their own implementation (could as well be a macro that generates something native or just a normal rest-arg method if/when we have #9274).

[Simn]

Last time I tried this I ran into the problem that a trace definition would have to support both rest arguments and the trailing haxe.PosInfos optional argument, which doesn't really fit together.