[IR] Extend test coverage for smart cast handling.

compiler/testData/ir/irText/expressions/whenSmartCastToEnum.kt.txt

@@ -0,0 +1,56 @@
+enum class En : Enum<En> {
+  private constructor() /* primary */ {
+    super/*Enum*/<En>()
+    /* <init>() */
+
+  }
+
+  A = En()
+
+  B = En()
+
+  C = En()
+
+  fun values(): Array<En> /* Synthetic body for ENUM_VALUES */
+
+  fun valueOf(value: String): En /* Synthetic body for ENUM_VALUEOF */
+
+}
+
+fun test() {
+  var r: String = ""
+  val x: Any? = En.A
+  when {
+    x is En -> { // BLOCK
+      { // BLOCK
+        val tmp0_subject: En = x /*as En */
+        when {
+          EQEQ(arg0 = tmp0_subject, arg1 = En.A) -> { // BLOCK
+            r = "when1"
+          }
+          EQEQ(arg0 = tmp0_subject, arg1 = En.B) -> { // BLOCK
+          }
+          EQEQ(arg0 = tmp0_subject, arg1 = En.C) -> { // BLOCK
+          }
+        }
+      }
+    }
+  }
+  val y: Any = En.A
+  when {
+    y is En -> { // BLOCK
+      { // BLOCK
+        val tmp1_subject: En = y /*as En */
+        when {
+          EQEQ(arg0 = tmp1_subject, arg1 = En.A) -> { // BLOCK
+            r = "when2"
+          }
+          EQEQ(arg0 = tmp1_subject, arg1 = En.B) -> { // BLOCK
+          }
+          EQEQ(arg0 = tmp1_subject, arg1 = En.C) -> { // BLOCK
+          }
+        }
+      }
+    }
+  }
+}