Support notification progress instead of only status bar

While investigating a bug about progress notifications not showing during refactors, I found that this client always uses status bar notifications which are very subtle:

https://github.com/microsoft/vscode-languageserver-node/blob/0671381a338f496afdff98b43a2f2d38def468e7/client/src/common/progressPart.ts#L61-L62

While this is fine for something like background analysis, it's much less useful for something like an expensive refactor if a user drags a folder in explorer and it may take a few seconds to compute all the edits to update the imports. This would be better as a more visible notification.

@dbaeumer I'd be happy to implement this using middleware for my extension, but it's not clear if that's possible because this code lives inside ProgressPart.begin(). It would be nice to support it in the client though - maybe even the spec? I think the concept of a progress notification that is prominent because it is doing something important the user is explicitly waiting for could make sense (or, maybe the client could do it if the progress is tied to some kinds of requests, like executeCommand?).

Start with client/src/common/progressPart.ts at lines 61-62 and read ProgressPart.begin() to understand how progress is currently shown through status bar notifications. Investigate whether middleware or client/spec support can expose a more prominent notification for user-initiated, expensive operations; done means an agreed design and corresponding support for that progress behavior.