FIR DFA: x !is T? => x != null

^KT-22996 tag fixed-in-k2

compiler/tests-spec/testData/diagnostics/notLinked/dfa/neg/45.fir.kt

@@ -7,8 +7,8 @@
  */
 fun case_1(x: Number?): Long? {
     if (x is Long?) return x
-    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Number?")!>x<!>
-    return <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Number?")!>x<!><!UNSAFE_CALL!>.<!>toLong()
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Number? & kotlin.Number")!>x<!>
+    return <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Number? & kotlin.Number")!>x<!>.toLong()
 }
 
 /*