[Core] Improve OperationHelpers

[kinelski]

Currently our OperationHelpers class doesn't do much, and Long-Running Operation classes in general are very repetitive. Most of the logic could be shared.

Goals

• Move repetitive bits to the OperationHelpers class.
• If possible, write OperationHelpers in a way that ensures thread-safety (related discussion).
• Implement the polling in a way that:
  • The default polling time can be overwritten individually by each operation type.
  • The default polling time can be set to zero by our test framework to improve playback runs. If possible, avoid Reflection.
  • Look for the retry-after property returned by the service when deciding the next polling time.
• Make sure all Track 2 data plane libraries with LROs make use of the new OperationHelpers whenever possible. All these libraries are exhaustively listed below.
• Consider:
  • Keeping OperationHelpers as an extension class.
  • Making OperationHelpers as part of the Azure.Core library.
  • Implementing the OperationHelpers functionality as part of the abstract Operation<T> class.

Track 2 data plane libraries that make use of LROs

• FormRecognizer
• KeyVault.Administration
• KeyVault.Certificates
• KeyVault.Keys
• KeyVault.Secrets
• MixedReality.RemoteRendering
• Storage.Blobs
• Synapse.Spark
• TextAnalytics

Suggestion: we can use the ArmOperationHelpers class used by the resource manager libraries as a reference. Their LROs seem to follow a stricter pattern than the ones used in data plane libraries, so it may be a bit harder on our side.

[heaths]

+1 on checking the Retry-After header, which Key Vault does send and we're not using currently.