Fix async poller workflow slot used

[jjaegerman]

What was changed

• AsyncWorkflowPollTask calls markSlotUsed on the SlotSupplier when a task is received

Why?

• This is behavior that is present in WorkflowPollTask but missing in AsyncWorkflowPollTask
• This ensures that TrackingSlotSupplier's usedSlots gets updated when PollerBehaviorAutoscaling is enabled
• usedSlots is used to report WORKER_TASK_SLOTS_AVAILABLE
• This fixes the incorrect WORKER_TASK_SLOTS_AVAILABLE value problem described in the issue when PollerBehaviorAutoscaling is enabled

Note:

• markSlotUsed is handled by the worker Implementation for Activity and Nexus paths (instead of the poll task)
• This behavior cannot be easily moved from WorkflowPollTask to WorkflowWorker because WorkflowWorker cannot easily determine if the task is the result of a poll to a sticky task queue or normal task queue (needed for the fromStickyQueue field)

Checklist

1. Closes #2802

2. How was this tested: New SlotSupplierTest covers this case (this is where the equivalent synchronous WorkflowPollTask behavior is tested)

3. Any docs updates needed?
   No

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