In case the worker is in down 'exit' the host still accept requests till it time out

While @mhoeger and I working on #5361 we found that although the worker is down, the host still accepting requests till the function timeout.

When the worker is down, the host still accepts requests and SendInvocationRequest will be called and SendStreamingMessage
https://github.com/Azure/azure-functions-host/blob/3eb520c7e7946dd2ebaca6fa00ef2562d86fde00/src/WebJobs.Script/Workers/Rpc/RpcWorkerChannel.cs#L328

**but the OutboundEvent will not be triggered from**

https://github.com/Azure/azure-functions-host/blob/398f8264f2d579a71d31ba3f59a442afbbdef643/src/WebJobs.Script/Workers/Rpc/FunctionRpcService.cs#L61

Start in src/WebJobs.Script/Workers/Rpc/RpcWorkerChannel.cs around the SendInvocationRequest and SendStreamingMessage call, then compare it with the OutboundEvent handling in src/WebJobs.Script/Workers/Rpc/FunctionRpcService.cs. Reproduce the worker-down path described in the issue and trace why the request remains accepted. Done means requests fail promptly when the worker exits instead of waiting for the function timeout.

Written by the indexing model from the issue text.