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/linkTest_lib.kt

@@ -0,0 +1,7 @@
+package a
+
+enum class A(val x: Int) {
+    Z1(42),
+    Z2(117),
+    Z3(-1)
+}