Socket.SendFileAsync based on SendPacketsAsync (#52208)

Socket.SendFileAsync based on SendPacketsAsync (#52208)

* Socket.SendFileAsync layered on top of SendPacketsAsync

* Tests

* Cleanup

* Set SendPacketsFlags

* Check if the socket is connection orientated

Cf. https://github.com/dotnet/runtime/pull/52208#discussion_r625922176

* Try to re-use the SendPacketsElement-array

Cf. https://github.com/dotnet/runtime/pull/52208#discussion_r625346014

* Fixed test

Cf. https://github.com/dotnet/runtime/pull/52208#discussion_r625316709

* Update src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs