Background

Continuing on from making disposing async, we need to make disposal with using statements become async.

Results

Before

Whenever something that supports async operations is disposed, it does the disposal synchronously on the thread. This blocks the thread if disposal involves things like IO.

After

We now try to use await using instead of using do that any asynchronous operations done during disposal will no longer block the calling thread.

.NET 4.8 Complications

Streams in .NET 4.8 do not support IAsyncDisposable. This means we cannot add await to using statements.

This was fixed by wrapping the await in a #if

RewindableBufferStream

We also made RewindableBufferStream implement IAsyncDisposable. This allowed us to using await using whenever we interacted with this type of stream.

Using Our Streams

We made all our streams extend IAsyncDisposable so that they would work in .NET 4.8 with await using

How to review this PR

Quality :heavy_check_mark:

Pre-requisites

[ ] I have read How we use GitHub Issues for help deciding when and where it's appropriate to make an issue.
[ ] I have considered informing or consulting the right people, according to the ownership map.
[ ] I have considered appropriate testing for my change.