[Feature Request] Support IAsyncDisposable activity classws with async scopes for DI in .NET 6+

[cretz]

Describe the solution you'd like

Currently we don't support IAsyncDisposable instances of activity classes when using the Temporalio.Extensions.Hosting DI because we create synchronous scopes.

Change

sdk-dotnet/src/Temporalio.Extensions.Hosting/ServiceProviderExtensions.cs

Line 64 in 3faaf2b

using (var scope = provider.CreateScope())

to await using (var scope = provider.CreateAsyncScope()), but there may need to be compiler directives since it's .NET 6+ (and we may have to distribute a .NET-6-specific version of this library)

[cretz]

Handled with #207