Optimize classSymbol of AppliedTypes

Try underlying first, since it is fastest for uncached types.

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -500,6 +500,13 @@ object Types {
       case tp: TypeRef =>
         val sym = tp.symbol
         if (sym.isClass) sym else tp.superType.classSymbol
+      case tp: AppliedType =>
+        val cls = tp.underlying.classSymbol
+        if cls == defn.AnyClass
+          // in that case, `tp` could be a type alias the reduces to an argument;
+          // need to go through dealias
+        then tp.superType.classSymbol
+        else cls
       case tp: TypeProxy =>
         tp.superType.classSymbol
       case tp: ClassInfo =>