Consolidate provisioning related protobuf parsing

[ Merge of http://go/wvgerrit/87905 ]

Protobuf parsing of the provisioning message has been centralized in
certificate_provisioning.cpp since it will be invoked from
multiple locations. This will also ease maintainability of the code.

Bug: 142731300
Test: android unit/integration tests
Change-Id: Idebf6b0145b317698559cac1cf18a3a0b98315ad

libwvdrmengine/cdm/core/include/certificate_provisioning.h

@@ -48,6 +48,19 @@ class CertificateProvisioning {
       FileSystem* file_system, const CdmProvisioningResponse& response,
       std::string* cert, std::string* wrapped_key);
 
+  // Helper methods
+
+  // Extract serial number and system ID from a DRM Device certificate.
+  // Either |serial_number| or |system_id| may be null, but not both.
+  static bool ExtractDeviceInfo(const std::string& device_certificate,
+                                std::string* serial_number,
+                                uint32_t* system_id);
+
+  // Removes json wrapping if applicable to extract the
+  // SignedProvisioningMessage
+  static bool ExtractAndDecodeSignedMessageForTesting(
+      const std::string& provisioning_response, std::string* result);
+
  private:
   CdmResponseType SetSpoidParameter(
       const std::string& origin, const std::string& spoid,