[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/smartCasts/variables/ifVarIs.fir.kt

@@ -0,0 +1,9 @@
+public fun bar(s: String) {
+    System.out.println("Length of $s is ${s.length}")
+}
+
+public fun foo() {
+    var s: Any = "not null"
+    if (s is String) 
+        bar(s)
+}