Update-with-start

[dandavison]

This PR adds an API for "update-with-start", using the MultiOperation gRPC API.

PR is in draft mode because the test suite is incomplete, but please feel free to review the API and implementation.

The following code demonstrates the API and is taken from the early-return sample:

  const startWorkflowOperation = new WithStartWorkflowOperation(transactionWorkflow, {
    workflowId,
    args: [transactionID],
    taskQueue: 'early-return',
    workflowIdConflictPolicy: 'FAIL', // required
  });

  const earlyConfirmation = await client.workflow.executeUpdateWithStart(getTransactionConfirmation, {
    startWorkflowOperation,
  });
  const wfHandle = await startWorkflowOperation.workflowHandle();
  const finalReport = await wfHandle.result();

Public API

• New client interceptor startUpdateWithStart with interfaces WorkflowStartUpdateWithStartInput and WorkflowStartUpdateWithStartOutput
• New class WithStartWorkflowOperation
• WorkflowClient.executeUpdateWithStart and WorkflowClient.startUpdateWithStart

[dandavison]

This is a bug fix against basic Update. Previously, if waitStage=Completed we were issuing UpdateWorkflow requests after the update has reached Accepted. But that is not what we should do: we should issue UpdateWorkflow until Accepted and then switch to PollWorkflowUpdate. All other SDKs do this.