Java to Kotlin converter: correct nullability in signatures of overrides

#KT-5269 Fixed

j2k/tests/testData/ast/nullability/OverrideWithInheritanceLoop.kt

@@ -0,0 +1,9 @@
+class A() : B() {
+    public fun foo(s: String) {
+    }
+}
+
+class B() : A() {
+    public fun foo(s: String) {
+    }
+}