Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/anonymousObject/kt6552.kt

@@ -0,0 +1,18 @@
+// FILE: 1.kt
+
+package test
+
+public enum class X { A, B }
+
+public inline fun switch(x: X): String = when (x) {
+    X.A -> "O"
+    X.B -> "K"
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun box(): String {
+    return switch(X.A) + switch(X.B)
+}