[SwiftBindings] Allow C# types to be passed to Swift generic functions with protocol constraints

[jkurdek]

User should be able to implement a C# type which conforms to a projected Swift Protocol. Then it should be possible to use this type whenever calling swift generic functions who accept a generic argument constrained to the implemented protocol.

The C# type will not have a valid protocol witness table with respect to the Swift protocol, which means that it cannot be directly passed to generic functions/types. We will most likely need some proxy