Migrate boxAgainstJava tests to multi-file framework

compiler/testData/codegen/boxAgainstJava/sam/adapters/constructor.kt

@@ -1,5 +1,21 @@
+// FILE: JavaClass.java
+
+class JavaClass {
+    private Runnable r;
+
+    public JavaClass(Runnable r) {
+        this.r = r;
+    }
+
+    public void run() {
+        r.run();
+    }
+}
+
+// FILE: 1.kt
+
 fun box(): String {
     var v = "FAIL"
     JavaClass { v = "OK" }.run()
     return v
-}
+}