Add Clear() to IConfigurationBuilder

[davidfowl]

This will make it possible to remove all registered providers and start over. Specifically, when using WebHost.CreateDefaultBuilder(), this would allow application code to change all previously configured options without losing the other benefits of calling that method.

/cc @glennc @divega @DamianEdwards @ajcvickers @HaoK

[DamianEdwards]

Love it. Are there equivalents on the other builders we should also consider?

[HaoK]

For the behavior, would Clear only clear the config sources, or also clear the Properties metadata that stores the base path/default file provider as well?

Maybe we should just change Sources to be an IList<IConfigurationSource> instead of IEnumerable, so people can clear/rearrange as desired, they already can modify Properties directly since its exposed as an Dictionary<string, object> Properties (??) already

https://github.com/aspnet/Configuration/blob/dev/src/Microsoft.Extensions.Configuration.Abstractions/IConfigurationBuilder.cs

[HaoK]

I think in the past maybe we had special logic in Add, but its just a straight add now, so there's nothing that prevents us from exposing the ability for people to directly add to the sources

https://github.com/aspnet/Configuration/blob/dev/src/Microsoft.Extensions.Configuration/ConfigurationBuilder.cs#L38

[davidfowl]

Maybe it should implement IList or ICollection

[shirhatti]

We discussed this in triage and we want Sources to be an IList<IConfigurationSource>

[davidfowl]

@HaoK This is fixed right?

[HaoK]

Yup, fixed via 6b4f1f8