Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/reflection/referenceToJavaFieldOfKotlinSubclass.kt

@@ -0,0 +1,15 @@
+// FILE: J.java
+
+public class J extends K {
+    public final int value = 42;
+}
+
+// FILE: K.kt
+
+open class K
+
+fun box(): String {
+    val f = J::value
+    val a = J()
+    return if (f.get(a) == 42) "OK" else "Fail: ${f.get(a)}"
+}