Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/innerGenericClass.kt

@@ -0,0 +1,25 @@
+// FILE: JavaClass.java
+
+public abstract class JavaClass {
+    public static String test() {
+        return Test.INSTANCE.foo(new Outer<String>("OK").new Inner<Integer>(1));
+    }
+}
+
+// FILE: Kotlin.kt
+
+class Outer<E>(val x: E) {
+    inner class Inner<F>(val y: F) {
+        fun foo() = x.toString() + y.toString()
+    }
+}
+
+object Test {
+    fun foo(x: Outer<String>.Inner<Integer>) = x.foo()
+}
+
+fun box(): String {
+    val result = JavaClass.test()
+    if (result != "OK1") return "Fail: $result"
+    return "OK"
+}