New J2K: add multi-file conversion tests from old j2k

nj2k/testData/multiFile/GetterAndSetterUsages/2.kt

@@ -0,0 +1,11 @@
+package test
+
+class B {
+    fun foo(a: AAA) {
+        a.x = a.x + 1
+        yY += "a"
+    }
+
+    var yY = ""
+        private set
+}