[ Merge of http://go/wvgerrit/106203 ]
CdmSigningAlgorithm are converted into OEMCrypto_Algorithm enums
before being passed as parameters to OEMCrypto generic crypto functions.
The OEMCrypto_Algorithm variables should never be set to values not
specified in the enum declaration.
These private methods have also been moved to the anonymous namespace.
Bug: 168774486
Test: WV unit/integration tests
Change-Id: Ie570a3cf4447b6c133076baa0909d562824c8e4a