Add tests for DataContractSerializer serializing BindingList types

[huanwu]

We need have tests covering DataContractSerializer serializing the following type.
Refer https://github.com/dotnet/corefx/blob/master/src/System.Runtime.Serialization.Xml/tests/DataContractSerializer.cs on how to add the DCS tests using the common helper method.
#21982

• System.ComponentModel.BindingList`1[[System.Runtime.Serialization.Formatters.Tests.Point]]

[safern]

@huanwu any update moving to future as this doesn't seem like a high pri for 2.1

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