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

compiler/testData/diagnostics/tests/smartCasts/loops/useInsideDoWhile.fir.kt

@@ -0,0 +1,9 @@
+public fun foo(p: String?, y: String?): Int {
+    do {
+        // After this !!, y. should be smartcasted in loop as well as outside
+        y!!.length
+        if (p == null) break
+        y.length
+    } while (true)
+    return y.length
+}