[FIR] Support PreliminaryLoopVisitor in FIR DFA

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

@@ -13,5 +13,5 @@ fun list(start: String) {
         e = e.next()
     }
     // e can never be null but we do not know it
-    e.hashCode()
-}
+    e<!UNSAFE_CALL!>.<!>hashCode()
+}