Add vts tests to verify DRM AIDL interface

The DRM AIDL interface is in change 15329852.
The default implementation of the interface is in the clearkey
HAL in change 15958954.

[TODO] APIs pending vts coverage:
+ ICryptoFactory
   + isCryptoSchemeSupported
+ ICryptoPlugin
   + getLogMessages
   + notifyResolution
   + requiresSecureDecoderComponent
+ IDrmFactory
   + getSupportedCryptoSchemes
   + isContentTypeSupported
+ IDrmPlugin
   + decrypt
   + encrypt
   + getLogMessages
   + getMetrics
   + getNumberOfSessions
   + getPropertyByteArray
   + getPropertyString
   + getSecureStop
   + getSecureStopIds
   + getSecureStops
   + queryKeyStatus
   + releaseAllSecureStops
   + releaseSecureStop
   + releaseSecureStops
   + removeAllSecureStops
   + removeKeys
   + removeSecureStop
   + requiresSecureDecoder
   + requiresSecureDecoderDefault
   + restoreKeys
   + setCipherAlgorithm
   + setMacAlgorithm
   + setPlaybackId
   + setPropertyByteArray
   + sign
   + signRSA
   + verify

Bug: 170964303
Bug: 200055138
Test: atest VtsAidlHalDrmTargetTest
Change-Id: If8b582796fdbc34d3d7720fa45df8291f72cd46a