(1) Change wv_cas_ecm to allow 16 bytes of content_iv

(2) Remove "wrapping_iv" parameters from wv_cas_ecm
(3) Internally derive "wrapping_iv"s and "key_id"s
(4) Add an example binary for demo the usage of wv_cas_ecm

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218209010

common/crypto_util.h

@@ -49,6 +49,9 @@ std::string DeriveKey(absl::string_view key, absl::string_view label,
 // Derives an IV from the provided |context|.
 std::string DeriveIv(absl::string_view context);
 
+// Derives a key ID from the provided |context|.
+std::string DeriveKeyId(absl::string_view context);
+
 // Helper function to derive a key using the group master key and context.
 std::string DeriveGroupSessionKey(absl::string_view context, const uint32_t size_bits);