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

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

@@ -0,0 +1,9 @@
+fun main() {
+    var result: String? = null
+    var i = 0
+    while (result == null) {
+        if (i == 10) result = "non null"
+        else i++
+    }
+    result.<!INAPPLICABLE_CANDIDATE!>length<!>
+}