[Test] Properly merge box against java testdata into codegen/box

Previous commit about it was 3199ce03 and it was completely wrong

compiler/testData/codegen/box/interfaces/defaultMethod.kt

@@ -0,0 +1,25 @@
+// DONT_TARGET_EXACT_BACKEND: JS JS_IR JS_IR_ES6 WASM NATIVE
+// JVM_TARGET: 1.8
+
+// MODULE: lib
+// FILE: A.java
+
+public interface A {
+    default String getMessage() {
+        return "OK";
+    }
+}
+
+// MODULE: main(lib)
+// FILE: 1.kt
+
+interface I : A
+
+class B : A
+
+open class C(a : A) : I, A by a
+
+fun box(): String {
+    val a = B()
+    return C(a).message
+}