Add test for smartcast

idea/idea-completion/testData/basic/common/primitiveCompletion/smartCast.kt

@@ -0,0 +1,21 @@
+interface A {
+    fun a()
+}
+
+interface B {
+    fun b()
+}
+
+interface C {
+    fun c()
+}
+
+fun take(a: A) {
+    if (a is B && a is C) {
+        a.<caret>
+    }
+}
+
+// EXIST: a
+// EXIST: b
+// EXIST: c