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

compiler/testData/diagnostics/tests/smartCasts/publicVals/simple.fir.kt

@@ -0,0 +1,12 @@
+public class X {
+    public val x : String? = null
+    public fun fn(): Int {
+        if (x != null)
+            // Smartcast is possible because it's value property with default getter
+            // used in the same module
+            return x.length
+        else
+            return 0
+    }
+}
+