Remove System.Linq.Async dependency

[ob-stripe]

r? @remi-stripe
cc @stripe/api-libraries

Remove the dependency on System.Linq.Async, by reimplementing the .ToEnumerable() method directly.

Fixes #1974.

[ob-stripe]

The source code is basically a copy/paste from System.Linq.Async's implementation: https://github.com/dotnet/reactive/blob/7ad606b3dcd4bb2c6ae9622f8a59db7f8f52aa85/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToEnumerable.cs

[ob-stripe]

Sorry for force-pushing mid review :( I moved most of the code into AsyncUtils.

[brandur-stripe]

LGTM.

Thanks for adding that remark on code borrowing — was just about to ask for something similar :)

[ob-stripe]

Thanks Brandur!

[ob-stripe]

Released as 35.11.1.

[clement911]

This code is a bit weird, they even mentioned it's an anti pattern.

Async over sync is often worse than just sync so another option would be to have the !NET45 ListRequestAutoPaging used the same implementation as the ListRequestAutoPaging used fo NET45 instead of doing sync over ListRequestAutoPagingAsync.. Then you could remove AsyncUtils altogether.

Just a suggestion...

[ob-stripe]

Yeah, I was a little bit on the fence about it. The autopagination implementation is complex enough that I'd rather avoid duplicating the method, so I went with this.

(Of course right now the implementation is duplicated anyway because of NET45, but we will likely drop support for .NET Framework < 4.6.1 at some point.)

[clement911]

Looks like it might cause deadlocks #1946 (comment)