Optimize WhiskEntity deserialization

Currently the deserialization logic for `WhiskEntity` uses a trail based approahc where it tries multiple deserializers

https://github.com/apache/openwhisk/blob/e9dd2073cd2343545d006cd71ca01dc24114c216/common/scala/src/main/scala/org/apache/openwhisk/core/entity/WhiskEntity.scala#L134-L152

This can be optimized for newer setups which started using new `entityType` attribute (#3164). So we can have a pre check if the object have field `entityType` defined then use that otherwise fallback to existing approach.

It would avoid the cost of exception generated for cases where we are looking for entries later in the sequence

Start in common/scala/src/main/scala/org/apache/openwhisk/core/entity/WhiskEntity.scala, especially lines 134-152, and trace the current trail-based deserialization. Verify how entityType is represented and where the fallback is used; done means newer entities avoid the exception-driven attempts while entities without entityType retain the existing behavior.

Written by the indexing model from the issue text.