Migrate CompileKotlinAgainstKotlin test to multi-file framework

compiler/testData/compileKotlinAgainstKotlin/nestedObject.kt

@@ -0,0 +1,18 @@
+// FILE: A.kt
+
+package aaa
+
+class A {
+    object O {
+      val s = "OK"
+    }
+}
+
+// FILE: B.kt
+
+fun main(args: Array<String>) {
+    val str = aaa.A.O.s
+    if (str != "OK") {
+        throw Exception()
+    }
+}