Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/complexStack/asCheck.kt

@@ -0,0 +1,28 @@
+// FILE: 1.kt
+
+package test
+
+object ContentTypeByExtension {
+    inline fun processRecords(crossinline operation: (String) -> String) =
+            listOf("O", "K").map {
+                val ext = B(it)
+                operation(ext.toLowerCase())
+            }.joinToString("")
+}
+
+
+
+
+inline fun A.toLowerCase(): String = (this as B).value
+
+open class A
+
+open class B(val value: String) : A()
+
+// FILE: 2.kt
+
+import test.*
+
+fun box(): String {
+    return ContentTypeByExtension.processRecords { ext -> ext }
+}