Commented Feature: Enum support in WebApi [1584]

WebApi treats Enum type as String and processes Enum type specially.
Since OData V4 supports Enum type, we want to support Enum type in WebApi after OData migrates to V4.
ODataModelBuilder, ODataConventionModelBuilder, serialization, deserialization and query should be modified to support this feature.
Comments: Checkin: Enum support for Action and Function 79dc98598c9b2227d6cc666d7e79915ab723ec4e