Fix SignalR Server's usage of MakeGenericMethod when using a streaming reader (IAsyncEnumerable or ChannelReader) following the same approach as the client. Add a runtime check and throw an exception when trying to stream a ValueType in native AOT.

Adjust the public annotations:
* Remove RequiresUnreferencedCode from AddSignalR
* Add RequiresUnreferencedCode to MessagePack and NewtonsoftJson protocols

Support trimming and AOT in DefaultHubDispatcher by adding a feature switch to turn off custom awaitable support.
Update ObjectMethodExecutor to support trimming and AOT by a new method that doesn't look for custom awaitables, and uses reflection instead of Linq.Expressions.

* Move RequiresDynamicCode to the whole Hub<T> class, so developers always get a warning when using IHubContext<THub, T>. This helps because THub needs to be a Hub<T>, which will warn as soon as it is used.
* Suppress the warning in AddSignalRCore that references HubContext<THub, T> since users will get warnings when they try using IHubContext<THub, T>.

… other feature switch naming