Add default update handler

[THardy98]

Added ability to register a default update handler. The default handler will handle updates with names that have no registered handler.

1. Part of [Feature Request] Support dynamic workflows, activities, signals, queries, and updates #1015

2. How was this tested:
   Added a couple activation tests with some comments describing the semantics of update code.

3. Any docs updates needed?
   Maybe

[mjameswh]

Shouldn't the second argument of toPayloads be an array? If so, the input argument should be unknown[] instead of just unknown.

[THardy98]

Yes, but input is a rest parameter in toPayloads, its a variadic function. I've changed it anyways for consistency.

[mjameswh]

To be exact, it is sync until the point where we actually call the update handler (i.e. the execute(input) call in doUpdateImpl(). By specification, the update validation must be executed sync, and the workflow handler function must be called immediately after. Otherwise, the workflow's internal state could be modified between the validation and the execute functions, and the validation result could be no longer valid by the time the execute function is called.

And in the specific case of this Workflow, the update handler is purely sync (i.e. there is no promise awaited on that code path), so it will also execute synchronously.

[THardy98]

I'm confused.

By specification, the update validation must be executed sync, and the workflow handler function must be called immediately after. Otherwise, the workflow's internal state could be modified between the validation and the execute functions, and the validation result could be no longer valid by the time the execute function is called.

This makes sense to me.

But how can the code be sync up until we call the execute call?

  /** Alias to `new UpdateScope({ id, name }).run(fn)` */
  static updateWithInfo<T>(id: string, name: string, fn: () => Promise<T>): Promise<T> {
    return new this({ id, name }).run(fn);
  }

UpdateScope.updateWithInfo(updateId, name, doUpdateImpl)

This is the async call at the end of doUpdate, it returns a promise.
doUpdateImpl itself is an async function as well.
How could these async calls guarantee sync execution till we execute the handler?

This is irrespective of the update handler code (async or not).

[mjameswh]

AFAICS, in the case of this specific workflow, doUpdateImplA will not get queued on node's event queue because there's no promise that is awaited from that update handler. Same for updateB.

[THardy98]

doUpdateImplA is async though, so I thought differently. Maybe we should coalesce this conversation into the other comment.