IR KT-50258 rewrite enum-based 'when' more carefully

compiler/testData/codegen/bytecodeText/whenEnumOptimization/nestedWhenInCondition.kt

@@ -0,0 +1,22 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// FIR_STATUS: FIR+JVM_IR generates TABLESWITCH for nested 'when' only, doesn't look critical.
+
+// JVM_IR_TEMPLATES
+// 2 (TABLE|LOOKUP)SWITCH
+
+enum class ABCD {
+    A, B, C, D
+}
+
+fun test(x: ABCD, y: ABCD, ok: String): String =
+    when (x) {
+        when (y) {
+            ABCD.A -> ABCD.B
+            ABCD.B -> ABCD.C
+            ABCD.C -> ABCD.D
+            ABCD.D -> ABCD.A
+        } ->
+            ok
+        ABCD.A, ABCD.B, ABCD.C, ABCD.D ->
+            x.toString()
+    }