Return null system ID for built-in DRM cert devices.

[ Merge of http://go/wvgerrit/153489 ]

OEMCrypto does not provide an API for retrieving the system ID when
the TEE uses a built-in DRM certificate (provisioning 1.0).  New OEMs
and Android devices do not use prov 1.0; however, the Zimperium CDM
(at least the tests) use a built-in certificate and are failing
certain tests because of the missing system ID.  To address this
failure; the CDM SystemIdExtractor has been updated to return a null
system ID.

Bug: 235879962
Test: system_id_extractor_unittest
Change-Id: Ib4c2bd75a7825967b0aa9e31e144184ae18fe8fb

libwvdrmengine/cdm/core/src/system_id_extractor.cpp

@@ -60,8 +60,12 @@ bool SystemIdExtractor::ExtractSystemId(uint32_t* system_id) {
   bool success = false;
   switch (type) {
     case kClientTokenDrmCert:
-      LOGE("Cannot get a system ID from a DRM certificate");
-      return false;
+      LOGW(
+          "Cannot get a system ID from a DRM certificate, "
+          "using null system ID: security_level = %s",
+          RequestedSecurityLevelToString(security_level_));
+      *system_id = NULL_SYSTEM_ID;
+      return true;
     case kClientTokenKeybox:
       success = ExtractSystemIdProv20(system_id);
       break;