Initial v17 Release

Headers and Unit tests have been updated to match the v17 spec.

Documentation can be found here:
https://developers.devsite.corp.google.com/widevine/drm/client/oemcrypto/v17

util/include/wv_attributes.h

@@ -0,0 +1,16 @@
+// Copyright 2021 Google LLC. All rights reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine
+// License Agreement.
+
+#ifndef WVCDM_UTIL_WV_ATTRIBUTES_H_
+#define WVCDM_UTIL_WV_ATTRIBUTES_H_
+
+#ifndef UNUSED
+#  if defined(__GNUC__) || defined(__clang__)
+#    define UNUSED __attribute__((__unused__))
+#  else
+#    define UNUSED
+#  endif
+#endif
+
+#endif  // WVCDM_UTIL_WV_ATTRIBUTES_H_