Implement MediaDrm offline license support in Widevine hidl service.

Merged from http://go/wvgerrit/69723.

The new APIs are getOfflineLicenseIds, getOfflineLicenseState and
removeOfflineLicense. These methods are currently stubbed out in
Widevine hidl service. This CL completes the implementation.

Test: unit tests - libwvdrmdrmplugin_hidl_test

Test: GTS
  --test com.google.android.media.gts.MediaDrmTest#testWidevineApi29

bug: 117570686
Change-Id: I96ffb75f453e36e931effefd3664b5faa8d69d30

libwvdrmengine/cdm/core/include/cdm_engine.h

@@ -212,6 +212,17 @@ class CdmEngine {
                                             CdmSecurityLevel security_level,
                                             const std::string& key_set_id);
 
+  // Get offline license status: active, release or unknown
+  virtual CdmResponseType GetOfflineLicenseState(
+      const std::string& key_set_id,
+      CdmSecurityLevel security_level,
+      CdmOfflineLicenseState* license_state);
+
+  // Remove offline license with the given key_set_id
+  virtual CdmResponseType RemoveOfflineLicense(
+      const std::string& key_set_id,
+      CdmSecurityLevel security_level);
+
   // Usage related methods for streaming licenses
   // Retrieve a random usage info from the list of all usage infos for this app
   // id.