SerializeFlags is a namespace.

The SerializeFlags becomes a namespace that contains
the original class definition under type SerializeFlags::Type
and static constants.

Consequently, all SeralizeFlags methods can
now be constexpr.

Also added static tests.

Test: libvintf_test
Test: vintf_object_test
Bug: 110711640
Change-Id: I786a1f77e19defc2ab2d025de3ed7cfe48f4fbce
diff --git a/main.cpp b/main.cpp
index f766358..baac511 100644
--- a/main.cpp
+++ b/main.cpp
@@ -266,7 +266,7 @@
         std::cout << std::endl;
     }
 
-    SerializeFlags flags = SerializeFlags::EVERYTHING;
+    SerializeFlags::Type flags = SerializeFlags::EVERYTHING;
     if (!options.verbose) {
         flags = flags.disableHals().disableKernel();
     }