Distinct does not work on Enumerable<IEdmStructuredType>

[mhotze]

https://github.com/microsoft/OpenAPI.NET.OData/blame/c00a26b629e76d624f80911d4b97d9ae86af9cf7/src/Microsoft.OpenApi.OData.Reader/Generator/OpenApiSchemaGenerator.cs#L197 produces duplicates, when there is a navigation property to an entity that is already associate in the entity sets. In our case the EntityType is not the same instance, so it MUST be compared by FullName to get distinct values. I made the same mistake recently, so it would be nice if there is a default comparer.