Fix GetWorkerStopChannel() for Local Activities

[yuandrew]

What was changed

Plumb WorkerStopChannel through for Local Activities

Why?

Looks like this was never implemented to begin with

Checklist

1. Closes GetWorkerStopChannel no longer indicates worker shutdown for Local Activities #1963

2. How was this tested:

Changed a few tests to use this to avoid a race condition

3. Any docs updates needed?

[Quinn-With-Two-Ns]

Well the delay should be the graceful shutdown time no?

[Quinn-With-Two-Ns]

workerStopChannel should be closed during graceful shutdown and then the context should be cancelled when the graceful period elapse or the shutdown finished

[yuandrew]

hmm, looking at the graceful shutdown case, there is no delay.

but looking at TestLocalActivityWorkerShutdownNoHeartbeat, which I realized is non-graceful shutdown, we need a sleep. Otherwise, both LAs are able to complete before shutdown stops the LA.

[Quinn-With-Two-Ns]

hm for graceful shutdown there should be a delay between the channel closing and the context closing. The context shouldn't close during the graceful shutdown period

[yuandrew]

I was getting confused because the tests are doing different things. Added some comments to the tests to hopefully avoid any future confusion

For the non-graceful test, we want the LA to return context canceled err in order to test that we don't heartbeat on failure.

For the graceful tests, we want the LA to wait for shutdown to start before we complete, so when ctx is canceled doesn't matter in these tests

The context shouldn't close during the graceful shutdown period

I've separately confirmed that this is true.