Allow status of backup and restore operations to be queried

[heaths]

To facilitate long-running backup and restore operations, provide idiomatic APIs to query status. This may be on the KeyVaultBackupClient directly, or on public operation classes.

[christothes]

The possible statuses are InProgress, Succeeded, and Failed. IMO, The idiomatic mechanism to query status of an operation utilizing the standard set of properties is as follows:

• Evaluate the HasCompleted property of the operation
  • If true
    • Status = Succeeded: evaluating the Value property returns the result of the operation
    • Status = Failed: evaluating the Value property throws
  • If false
    • Status = InProgress
• Operation started in some other context
  • Hydrate the operation, given the Id of a previously started operation with this ctor
  • rules above apply

@heaths Were you thinking we should extend the operation classes to represent status more explicitly?

[heaths]

I should've been more clear. We need to expose a way to get the long-running Operation<T> classes after the fact, e.g. if the application was shut down but later restarted and needed to query status. The CertificateOperation in Certificates allows this via a constructor, taking the CertificateClient and certificate name. Something like that could be an option here as well.

[christothes]

I should've been more clear. We need to expose a way to get the long-running Operation<T> classes after the fact, e.g. if the application was shut down but later restarted and needed to query status. The CertificateOperation in Certificates allows this via a constructor, taking the CertificateClient and certificate name. Something like that could be an option here as well.

Perhaps I am missing something, but don't we have that here?

[heaths]

Maybe this didn't need opened then when I was doing all the langs - might've just been in err. However, those parameters need to flip. Client should go first, but I already opened a bug on that: #15065. Please make sure the restore operation is comparable.