Persist usage entry number

[ Merge of http://go/wvgerrit/23741 ]

Usage entries and usage entry numbers need to be stored with license
and usage information, to facilitate loading usage entries when offline
licenses/usage information are restored or prepared for release.

b/34327459

Test: Validated by running unit/integration tests on angler.

Change-Id: I0949fc4cec8a50be0a7700b659dc12bb82ac6f73

libwvdrmengine/cdm/core/src/device_files.proto

@@ -44,6 +44,7 @@ message License {
   // ignored if there is no grace period.
   optional int64 grace_period_end_time = 11 [default = 0];
   optional bytes usage_entry = 12;
+  optional int64 usage_entry_number = 13;
 }
 
 message UsageInfo {
@@ -53,6 +54,7 @@ message UsageInfo {
     optional bytes license = 3;
     optional bytes key_set_id = 4;
     optional bytes usage_entry = 5;
+    optional int64 usage_entry_number = 6;
   }
 
   repeated ProviderSession sessions = 1;