Update AnyView status in progress.md

[MaxDesiatov]

IDK, is there anything that SwiftUI AnyView can do that ours can't? ¯\_(ツ)_/¯

[j-f1]

There’s AnyView(erasing: View). I’m not sure if it’s actually behaviorally different but if not it should be an easy add.

[MaxDesiatov]

I think the erasing initializer is some kind of under the hood bugfix, it's marked as @_alwaysEmitIntoClient, the rest of the initializers are underscored.

For context:

@_alwaysEmitIntoClient is useful for keeping a particular declaration out of the ABI.