[Placeholder]Placeholders with out Run From Zip

[pragnagopa]

On FileChangeEvents, JobHost is restarted: https://github.com/Azure/azure-functions-host/blob/dev/src/WebJobs.Script.WebHost/FileMonitoringService.cs#L124

During specialization, JobHost is restarted here: https://github.com/Azure/azure-functions-host/blob/dev/src/WebJobs.Script.WebHost/Standby/StandbyManager.cs#L86

FunctionDispatcher uses a language worker process that is started in placeholder mode if one is available: https://github.com/Azure/azure-functions-host/blob/dev/src/WebJobs.Script/Rpc/FunctionRegistration/FunctionDispatcher.cs#L163

In order to support file edits for languages where user provides a script: python, nodejs and powershell , JobHost restart should recycle placeholder language worker process anytime file edits happen after specialization. But during specialization language worker process should not be killed.

Related issues #4511, #3415

cc: @fabiocav @mhoeger

[pragnagopa]

This will also unblock placeholders when using placeholder pools

[pragnagopa]

cc @mhoeger