Make ConfigurationOptions IDisposable

[philon-msft]

Creating this PR for discussion.

The main advantage of IDisposable ConfigurationOptions is it enables graceful shutdown of IDisposable default options providers like AzureCacheOptionsProviderWithToken, which has a token refresh Timer that should be stopped.

[NickCraver]

I'm not sure this makes sense given it doesn't own anything and a lot of people share options for the lifetime or for multiple multiplexers or pooling, so the IDE advice can be bad here instructing to dispose too.

I agree with the problem scenario, just don't think this is a good path to take trying to solve that category of stuff.

[mgravell]

The fact that the options and defaults provider often/usually have very different lifetimes makes this... awkward. It is not usually the cast that the two are linked, and most of the time this would be unnecessary and/or incorrect - making busy-work without need. I wonder whether there's some new wrapper API that we'd need instead, i.e.

public readonly struct NewWrapperNamingIsHard : IDisposable
{
    // wraps options+defaults provider

    public ConfigurationOptions Options => ...
    public static implicit operator ConfigurationOptions(NewWrapperNamingIsHard value) => value.Options;
}

so some API would return a NewWrapperNamingIsHard

[philon-msft]

Closing this. We'll use a different approach that relies on a new AfterDisconnectAsync() callback on DefaultOptionsProvider to shut down custom DefaultOptionsProviders when zero connections are using their ConfigurationOptions.