AIDL error handling

Starting in Android U (14), libmediadrm (app-side) understands extra error details from AIDL DRM HALs passed through the binder exception message as a json string. The supported fields are:

• cdmError (int)
• oemError (int)
• context (int)
• errorMessage (str)

The errors details will be reported to apps through the java interface android.media.MediaDrmThrowable. Please see the javadoc of MediaDrmThrowable for detailed definitions of each field above.