Add quick fixes for SMARTCAST_IMPOSSIBLE in 'if' #KT-27184 Fixed

idea/testData/quickfix/smartCastImpossibleInIfThen/ifThen2.kt

@@ -0,0 +1,10 @@
+// "Replace 'if' expression with safe access expression" "true"
+class Test {
+    var x: String? = ""
+
+    fun test() {
+        if (x != null) {
+            <caret>x.length
+        }
+    }
+}