Commented Unassigned: 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 ODataModelBuilder e28418dcd8142b2c7df6a64a08e92b2d190ddf50