KT-6118 Redundant type cast can be not redundant?

#KT-6118 Fixed

compiler/testData/diagnostics/tests/dataFlow/assignment/kt6118.kt

@@ -0,0 +1,16 @@
+// KT-6118 Redundant type cast can be not redundant?
+
+fun foo(o: Any) {
+    if (o is String) {
+        val s = o <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as String<!>
+        s.length()
+    }
+}
+
+fun foo1(o: Any) {
+    if (o is String) {
+        <!DEBUG_INFO_SMARTCAST!>o<!>.length()
+        val s = o
+        <!DEBUG_INFO_SMARTCAST!>s<!>.length()
+    }
+}