Make ValueTuple* binary serializable

[terrajobst]

We generally don’t want to add more types to be binary serializable in the framework, due to complexities and the fragility that it causes across version boundaries (remember that binary serialization has to be backward- and forward compatible). That being said, for ValueTuple we can likely convince ourselves that the serialization behavior is fixed and mostly a function of the types you instantiate the tuple with. It seems a resonable assumption to say that ValueTuple<T1, ..., TN> to be serializable if T1-TN are serializable.

Not being binary serializable also makes it harder (and more fragile) for existing code to switch from Tuple to ValueTuple.

[tarekgh]

CC @jcouv

[karelz]

API review: Approved.

[karelz]

@jcouv can you please do it? We need to change also Desktop.

[jcouv]

@karelz I'll stop by your office tomorrow to discuss and confirm.

[karelz]

@terrajobst will know more. I was just typing without too much context :)
But feel free to stop by and say hi ;-)

[jcouv]

Fixed in desktop, coreclr and corert. I think mono will pick this up automatically.
FYI @marek-safar just in case.