Migrate CompileKotlinAgainstKotlin test to multi-file framework

compiler/testData/compileKotlinAgainstKotlin/classInObject.kt

@@ -0,0 +1,15 @@
+// FILE: A.kt
+
+package a
+
+object CartRoutes {
+    class RemoveOrderItem()
+}
+
+// FILE: B.kt
+
+import a.CartRoutes
+
+fun main(args: Array<String>) {
+    val r = CartRoutes.RemoveOrderItem()
+}