Partially fix pickling tests failing with smarter tpd

This also seems to be a reason why Ycheck:front fails.

typeAssigner is REMOVING partial evaluation that typer did
when you copy a tree. It means that types would be different if
you test pickling.

Update made to homogenize:

- Don't print constant types in pickling.
- Sort union types according to their .show String

Author: OlivierBlanvillain

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

@@ -53,7 +53,10 @@ class PlainPrinter(_ctx: Context) extends Printer {
         case AndType(tp1, tp2) =>
           homogenize(tp1) & homogenize(tp2)
         case OrType(tp1, tp2) =>
-          homogenize(tp1) | homogenize(tp2)
+          if (tp1.show > tp2.show)
+            homogenize(tp1) | homogenize(tp2)
+          else
+            homogenize(tp2) | homogenize(tp1)
         case tp: SkolemType =>
           homogenize(tp.info)
         case tp: LazyRef =>

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -125,6 +125,8 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         ("implicit " provided isImplicit) ~ argStr ~ " => " ~ argText(args.last)
       }
     homogenize(tp) match {
+      case x: ConstantType if homogenizedView =>
+        return toText(x.widen)
       case AppliedType(tycon, args) =>
         val cls = tycon.typeSymbol
         if (tycon.isRepeatedParam) return toTextLocal(args.head) ~ "*"