KT-36047 Support when-with-subject in optimized 'when' generators

compiler/testData/codegen/bytecodeText/when/stringSwitchWithSubjectVal.kt

@@ -0,0 +1,12 @@
+fun foo(x: String): String {
+    return when (val y = x) {
+        "1" -> "one"
+        "2" -> "two"
+        "3" -> "two and one"
+        "4" -> "two and two"
+        else -> "many"
+    }
+}
+
+// 0 LOOKUPSWITCH
+// 1 TABLESWITCH