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

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

@@ -0,0 +1,11 @@
+fun x(): Boolean { return true }
+
+public fun foo(p: String?): Int {
+    // See KT-6283
+    do {
+        p!!.length
+    } while (!x())
+    // Do-while loop is executed at least once, so
+    // p should be not null here
+    return p.length
+}