[Test] Add test for KT-53460

compiler/testData/diagnostics/tests/nullableTypes/notUselessComparasionAfterSmartcast.fir.kt

@@ -0,0 +1,14 @@
+// ISSUE: KT-53460
+
+fun test(a: String?, b: String?) {
+    if (a == null || a == "foo") {
+        when (b) {
+            "abc" -> return
+        }
+    }
+
+    a<!UNSAFE_CALL!>.<!>length // should be an error
+    if (a == null || a == "bar") { // comparasion to null is not useless
+        a<!UNSAFE_CALL!>.<!>length
+    }
+}

compiler/testData/diagnostics/tests/nullableTypes/notUselessComparasionAfterSmartcast.kt

@@ -0,0 +1,14 @@
+// ISSUE: KT-53460
+
+fun test(a: String?, b: String?) {
+    if (a == null || a == "foo") {
+        when (b) {
+            "abc" -> return
+        }
+    }
+
+    <!DEBUG_INFO_SMARTCAST!>a<!>.length // should be an error
+    if (<!SENSELESS_COMPARISON!>a == null<!> || a == "bar") { // comparasion to null is not useless
+        <!DEBUG_INFO_SMARTCAST!>a<!>.length
+    }
+}