[Test] Move KotlinAgainstKotlin tests under BlackBoxCodegen tests

compiler/testData/codegen/box/compileKotlinAgainstKotlin/nestedObject.kt

@@ -0,0 +1,17 @@
+// MODULE: lib
+// FILE: A.kt
+
+package aaa
+
+class A {
+    object O {
+        val s = "OK"
+    }
+}
+
+// MODULE: main(lib)
+// FILE: B.kt
+
+fun box(): String {
+    return aaa.A.O.s
+}