Separate OEM unprovisioning from DRM unprovisioing.

[ Cherry-pick of v19 http://go/wvgerrit/219330 ]
[ Merge of http://go/wvgerrit/219454 ]

For two-staged provisioning devices, the behavior of
CdmEngine::Unprovision() varied by platform and context.
For production Android, unprovisioning would remove both;
for production and testing CE CDM it would only remove
DRM provisioning; for testing Android may remove both or
remove everything (both certs and licenses).

This behavior was not documented, making use of the
CdmEngine::Unprovision() API rather unpredictable.

This change attempts to document the unpredictable behavior
and add a way to explicitly remove the OEM certificate
in the core code.

The new CdmEngine::UnprovisionOemCert() will remove only
the OEM certificate.

Bug: 391469176
Test: run_x86_64_tests
Test: WvTs on oriole
Change-Id: Ib2f6ef61f45b5320c71d7e8e8460f7fe8e0e2248

libwvdrmengine/cdm/src/wv_content_decryption_module.cpp

@@ -346,6 +346,8 @@ CdmResponseType WvContentDecryptionModule::Unprovision(
   // Enable immediate OEMCrypto termination and re-initalization on
   // unprovisioning.
   CryptoSession::DisableDelayedTermination();
+  // Android unprovisioning has historically allowed for both
+  // DRM (app/origin-specific) and OEM (global) unprovisioning.
   return cdm_engine->Unprovision(level);
 }