When by String constants:

Generate TABLESWITCH/LOOKUPSWITCH bytecode operation for when operator by String constants

compiler/testData/codegen/bytecodeText/whenStringOptimization/denseHashCode.kt

@@ -0,0 +1,15 @@
+
+fun foo() : Int {
+    val x : String = "dsa"
+    when (x) {
+        "a" -> return 1
+        "b" -> return 1
+        "c" -> return 1
+        "d" -> return 1
+        "e" -> return 1
+        "f" -> return 1
+        else -> return -1
+    }
+}
+
+// 1 TABLESWITCH