Made TemporalWorker.ExecuteAsync() keep working even after Dispose().

[maciejdudko]

What was changed

Changed how resources are disposed inside TemporalWorker. If ExecuteAsync is called, then the Dispose method does nothing and instead the resources are disposed at the end of ExecuteAsync. If it's not called, then resources are disposed with Dispose call as normal.

Why?

Fixes crash that happens if TemporalWorker is disposed too early.

Checklist

1. Closes [Bug] Segfault/crash occurs when using tasks without await #500

2. How was this tested:
   Added testcase WorkflowWorkerTests.ExecuteWorkflowAsync_PrematureDispose_WorkflowCompletes

[cretz]

Looks good, nothing blocking (comments are mostly unimportant)

[cretz]

Should we not do this unless disposing is true? I guess it doesn't matter much, but it is a bit confusing to read

[cretz]

I believe I have confirmed that even in this situation:

public Task StartWorkerAsync()
{
    using var worker = new TemporalWorker(someOptions);
    // Note this does not take the disposer because code is not run
    // inside of this because it is "async" so it waits for first "await"
    return worker.ExecuteAsync(someToken);
    // worker is disposed here
}

var task = StartWorkerAsync();
await task;

The disposer is properly transfered before the ExecuteAsync call is returned. But yes it will be important for future SDK devs to make sure no yieldable await points are ever added before this line is called. Technically we can help with this by doing this in the outer ExecuteAsync calls and removing the async keyword from them, but I am fine with this too.

[cretz]

Suggested change

	private static TemporalWorkerOptions PrepareOptions<TWorkflow>(TemporalWorkerOptions options)
	private static TemporalWorkerOptions PrepareWorkerOptions<TWorkflow>(TemporalWorkerOptions options)

Pedantic, don't have to change