[K/N] Migrate most simple filecheck tests to new infra

^KT-62157


Merge-request: KT-MR-12376
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

compiler/testData/codegen/box/fileCheck/when.kt

@@ -0,0 +1,19 @@
+// TARGET_BACKEND: NATIVE
+// FILECHECK_STAGE: CStubs
+
+var i = 1
+// CHECK-LABEL: define %struct.ObjHeader* @"kfun:#box(){}kotlin.String"
+fun box(): String = when(i) {
+    0 -> "FAIL: 0"
+    1 -> "OK"
+    2 -> "FAIL: 2"
+    else -> "FAIL: else"
+}
+// CHECK: when_case
+// CHECK: when_next
+// CHECK: when_case1
+// CHECK: when_next2
+// CHECK: when_case3
+// CHECK: when_next4
+// CHECK: when_exit
+// CHECK: ret void