Clean up other core CDM logs.

[ Merge of http://go/wvgerrit/122613 ]

Further log clean up in the core CDM code.
- Changed several INFO logs to DEBUG and VERBOSE
- Added more identifiers to the DEBUG logs to help match resource
  associations
- Added more enum-to-string functions
- Unknown enum values will be formatted to contain their numeric
  value

Key areas improved are the UsageTableHeader and CdmSession.

Bug: 183576879
Test: CE CDM unittests
Change-Id: I2d11e714d419e0736d3e2f7a7668e8d36d7ef449

libwvdrmengine/cdm/core/include/device_files.h

@@ -66,6 +66,12 @@ class DeviceFiles {
     kLicenseNotPresent = kResponseTypeBase + 16,
   };
 
+  // Converts the different enum types to a human readable C-string for
+  // logging.
+  static const char* CertificateStateToString(CertificateState state);
+  static const char* CertificateTypeToString(CertificateType type);
+  static const char* ResponseTypeToString(ResponseType type);
+
   // CdmLicenseData represents all of the data that is stored in CDM
   // license file.  License data is uniquely keyed using |key_set_id|.
   struct CdmLicenseData {