[BUG][CSHARP][GENERICHOST] Write enum values in expected JSON format #213

Job	Run time
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 44s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 13s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	1m 14s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 9s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	3m 14s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	1m 11s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	1m 28s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	1m 48s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	1m 15s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 6s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	1m 28s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	1m 6s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 18s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	1m 5s
	20m 19s

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