[Mono.Security.Interface]: Improve synergy between `SslStream` and `IMonoSslStream...

[Mono.Security.Interface]: Improve synergy between `SslStream` and `IMonoSslStream` (#4756)

* [Mono.Security.Interface]: Improve synergy between `MonoTlsProvider`, `SslStream` and `IMonoSslStream`.

* Add `IMonoSslStream.SslStream` property; the `IMonoSslStream` is now only created my the `SslStream`
  constructor, so `SslStream` "owns" the `IMonoSslStream`.

* Add internal `MonoTlsProvider.CreateSslStreamInternal()`.

* `SslStream` does not need to implement any additional interfaces; we can do without after
   getting rid of the wrapper classes.

* Add internal `SslStream.CreateMonoSslStream(Stream,bool,MonoTlsProvider,MonoTlsSettings)`.

* `MonoTlsProvider.CreateSslStream()` implementations should use this new method.

* Remove ancient obsolete MonoTlsProviderFactory APIs.

* `HttpListener` and `HttpConnection` now use `SslStream` instead of `IMonoSslStream`.

* [System]: Cleanup internal TLS Provider registration.

* Make it build.