Make JavaDefined an AfterLoadFlags

It can't be a FromStartFlags since we don't know whether a top-level
class is Java-defined before completing it once.

Author: smarter

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

@@ -452,7 +452,7 @@ object Flags {
    *  is completed)
    */
   val AfterLoadFlags: FlagSet = commonFlags(
-    FromStartFlags, AccessFlags, Final, AccessorOrSealed, LazyOrTrait, SelfName)
+    FromStartFlags, AccessFlags, Final, AccessorOrSealed, LazyOrTrait, SelfName, JavaDefined)
 
 
   /** A value that's unstable unless complemented with a Stable flag */