Split AnnotaionParam into String and Constant Expression params

This is needed to support constant expression lazy evaluation.

Test: build hidl-gen, hidl_test
Test: build hidl-gen on mac :)

Change-Id: I5f38b0d2cbea5928408379bff7f282a2cd63d03b
diff --git a/Interface.cpp b/Interface.cpp
index 78d42ad..2acb5a0 100644
--- a/Interface.cpp
+++ b/Interface.cpp
@@ -838,7 +838,7 @@
                 const AnnotationParam *param =
                         annotation->getParam("next");
                 if (param != nullptr) {
-                    for (auto value : *param->getValues()) {
+                    for (const auto& value : param->getValues()) {
                         out << "next: " << value << "\n";
                     }
                 }