Improve test data format for SMAP codegen tests

Instead of comments in a Kotlin source file, add a .smap with the contents of
the source mapping data (and possible comments)

compiler/testData/codegen/boxInline/smap/inlineOnly/noSmap.kt

@@ -11,13 +11,15 @@ fun box(): String {
     return "KO".reversed()
 }
 
-//SMAP
-//noSmap.1.kt
-//Kotlin
-//*S Kotlin
-//*F
-//+ 1 noSmap.1.kt
-//NoSmap_1Kt
-//*L
-//1#1,14:1
-//*E
+// FILE: 2.smap
+
+SMAP
+2.kt
+Kotlin
+*S Kotlin
+*F
++ 1 2.kt
+_2Kt
+*L
+1#1,7:1
+*E