Allow default(ImmutableArray<T>) to be serialized

[Liversage]

ImmutableArray<T> is a value type and the default value will throw NullReferenceException when the Length property is read. The serializer will read this property to determine how many elements in the array should be written to the stream making it impossible to serialize default(ImmutableArray<T>).

This change ensures that default(ImmutableArray<T>) can be serialized without throwing a NullReferenceException. The value default(ImmutableArray<T>) is indicated by writing -1 as the length of the array to the stream. Note that ImmutableArray<T>.Empty has a length of 0 so the code is able to distinguish between the two values.

The deserializer will make a call to context.RecordObject. I do not quite understand the purpose of this call and if it is meaningful to do with a value type but I included it in the added code because it was already in the existing code.

I have added a test that verifies that default(ImmutableArray<T>) can round-trip when serialized.

[dnfclas]

All CLA requirements met.

[Liversage]

The functional check had a failed test:

UnitTests.ActivationsLifeCycleTests.ActivationCollectorTests.ActivationCollectorShouldNotCollectBusyActivationsSpecifiedInPerTypeConfiguration

with the following exception message:

System.Net.Sockets.SocketException : An attempt was made to access a socket in a way forbidden by its access permissions

It seems unlikely to me that my change caused a regression in this test but any advice on how to resolve it will be appreciated.

[ReubenBond]

@Liversage that exception message is prevalent on those old Jenkins machines - I think something kills the job/sockets sometimes. Nothing to worry about.

[ReubenBond]

Thank you, @Liversage!