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

idea/testData/quickfix/smartCastImpossibleInIfThen/ifThenElse.kt

@@ -0,0 +1,8 @@
+// "Replace 'if' expression with elvis expression" "true"
+class Test {
+    var x: String? = ""
+
+    fun test() {
+        val i = if (x != null) <caret>x.length else 0
+    }
+}