Consistent erasure for Java method signatures

Use Jave erasure to compute the result type part of Java method
signatures too. I don't think that two distinct non-bridge Java
overloads can only differ in their result type so this shouldn't fix
anything, but it's more consistent.

Author: smarter

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

@@ -3367,7 +3367,7 @@ object Types {
           case tp: ExprType => tp.signature
           case tp =>
             if tp.isRef(defn.UnitClass) then Signature(Nil, defn.UnitClass.fullName.asTypeName)
-            else Signature(tp, isJava = false)
+            else Signature(tp, isJava)
         this match
           case tp: MethodType =>
             val params = if (isErasedMethod) Nil else tp.paramInfos