Create a WvCasStatus to be used as return type of libraries in media_cas_packager_sdk.

Following example: []/video/widevine/export/provisioning_sdk/public/provisioning_status.h
and
[]/video/widevine/export/exported_root/util/status.h

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218918745

example/BUILD

@@ -47,7 +47,8 @@ cc_binary(
     name = "wv_cas_ecm_example",
     srcs = ["wv_cas_ecm_example.cc"],
     deps = [
-        "//base",
+        "@abseil_repo//absl/base:core_headers",
         "//media_cas_packager_sdk/public:wv_cas_ecm",
+        "//media_cas_packager_sdk/public:wv_cas_status",
     ],
 )

example/wv_cas_ecm_example.cc

@@ -12,6 +12,7 @@
 #include <string>
 
 #include "media_cas_packager_sdk/public/wv_cas_ecm.h"
+#include "media_cas_packager_sdk/public/wv_cas_status.h"
 
 const int kContentIvSize = 16;
 const bool kKeyRotationEnabled = true;
@@ -27,17 +28,21 @@ const char kEntitlementKey[] = "entitlement_key.................";  // 32 bytes
 
 int main(int argc, char **argv) {
   widevine::cas::WvCasEcm wv_cas_ecm;
-  bool status =
+  widevine::cas::WvCasStatus status =
       wv_cas_ecm.Initialize(kContentIvSize, kKeyRotationEnabled, kCryptoMode);
-  if (!status) {
-    std::cerr << "Failed to initialize WV CAS ECM, error." << std::endl;
+  if (status != widevine::cas::OK) {
+    std::cerr << "Failed to initialize WV CAS ECM, error: "
+              << widevine::cas::GetWvCasStatusMessage(status)
+              << std::endl;
   }
   std::string ecm;
   status = wv_cas_ecm.GenerateEcm(kEvenKey, kEvenContentIv16Bytes, kOddKey,
                                   kOddContentIv16Bytes, kEntitlementKeyId,
                                   kEntitlementKey, &ecm);
-  if (!status) {
-    std::cerr << "Failed to generate WV CAS ECM, error" << std::endl;
+  if (status != widevine::cas::OK) {
+    std::cerr << "Failed to generate WV CAS ECM, error: "
+              << widevine::cas::GetWvCasStatusMessage(status)
+              << std::endl;
   } else {
     std::cout << "ECM size: " << ecm.size() << std::endl;
     std::cout << "ECM bytes: ";