Count symbol redefinition on late compilation as symbol loading

For the purposes of the capability of flag mutation on completion.

Author: anatoliykmetyuk

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -331,9 +331,11 @@ class Namer { typer: Typer =>
 
       val sym =
         if (prev.exists) {
+          prev.startedLoading()
           prev.flags = flags1
           prev.info = infoFn(prev.asInstanceOf[S])
           prev.setPrivateWithin(privateWithin)
+          prev.finishedLoading()
           prev
         }
         else symFn(flags1, infoFn, privateWithin)