Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/simple/simpleEnum.kt

@@ -0,0 +1,27 @@
+// FILE: 1.kt
+
+package test
+
+enum class MyEnum {
+    K;
+
+    //TODO: KT-4693
+    inline fun <T> doSmth(a: T) : String {
+        return a.toString() + K.name
+    }
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun test1(): String {
+    return MyEnum.K.doSmth("O")
+}
+
+fun box(): String {
+    val result = test1()
+    if (result != "OK") return "fail1: ${result}"
+
+    return "OK"
+}