Haxe 4.2 features

[markknol]

It would be nice if we could have support for the new Haxe 4.2 features in HaxeDevelop

• Module-level fields Module-level static declarations (closes #7452) HaxeFoundation/haxe#8460
• Abstract classes and functions Abstract classes HaxeFoundation/haxe-evolution#69 / Support abstract modifier on classes and methods HaxeFoundation/haxe#9716
• Rest arguments using ... syntax Variable / Rest arguments HaxeFoundation/haxe#9961