Make homogenize apply HKApplys

The pickler doesn't unpickle to HKApply, as such - we need
to print them in their applied form.

Author: felixmulder

src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -55,6 +55,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
           homogenize(tp.info)
         case tp: LazyRef =>
           homogenize(tp.ref)
+        case HKApply(tycon, args) =>
+          tycon.dealias.appliedTo(args)
         case _ =>
           tp
       }