Rewrote enum lowering to support usage from other modules.

- Split up enum lowering into two stages: descriptors creation and IR creation.
- Added link stage test.
- Enum.valueOf() uses binary search instead of linear.

backend.native/tests/codegen/enum/values.kt

@@ -1,8 +1,11 @@
 enum class E {
+    E3,
     E1,
     E2
 }
 
 fun main(args: Array<String>) {
+    println(E.values()[0].toString())
     println(E.values()[1].toString())
+    println(E.values()[2].toString())
 }