Handling the return value from an orchestrator function in Custom Handler without `$return` binding difinition in function.json

#### What problem would the feature you're requesting solve? Please describe.
Now I'm trying to port [Durable Functions for Node.js](https://github.com/Azure/azure-functions-durable-js) for [Deno](https://deno.land/) and [azure-functions-deno-worker](https://github.com/anthonychu/azure-functions-deno-worker).

In the development, I found the following:

- Handling return value from an orchestrator function is needed to make Durable Functions work when `yield` is used in the function.
- In the case of built-in workers (Node.js), the functions host always handles the return value from the orchestrator function even though there is no `$return` binding definition in function.json for the function, as the following example.

```json
"bindings": [
{
"name": "context",
"type": "orchestrationTrigger",
"direction": "in"
}
]
```

The code is at this line.
https://github.com/Azure/azure-functions-host/blob/8596a27c5a3cf1c26546418fe8ac6bcf132f808b/src/WebJobs.Script.Grpc/Channel/GrpcWorkerChannel.cs#L577-L582

Meanwhile, in the case of Custom Handler, if there is no `$return` binding definition in function.json, the return value from the orchestrator function is ignored even though proper value returns from the function by using [`ReturnValue`](https://docs.microsoft.com/en-us/azure/azure-functions/functions-custom-handlers#response-payload).
According to this line, it is needed that both the return value and the `$return` binding definition are not `null`.

https://github.com/Azure/azure-functions-host/blob/8596a27c5a3cf1c26546418fe8ac6bcf132f808b/src/WebJobs.Script/Workers/Http/HttpScriptInvocationResultExtensions.cs#L31-L38

To make the function host handle the return value, I tried some `$return` binding definitions like the following binding definition, but I cannot find right binding definition to do that.

```json
"bindings": [
{
"name": "context",
"type": "orchestrationTrigger",
"direction": "in"
},
{
"type": "http", // or blank ""
"name": "$return",
"direction": "out"
}
]
```

#### Describe the solution you'd like
Could you please consider that the function host handles the return value from the function like the following example (which I confirmed) [at this line](https://github.com/Azure/azure-functions-host/blob/8596a27c5a3cf1c26546418fe8ac6bcf132f808b/src/WebJobs.Script/Workers/Http/HttpScriptInvocationResultExtensions.cs#L31-L38) if there is no way to return the value properly in order to work the orchestrator function in the custom handler?

```csharp
if (httpScriptInvocationResult.ReturnValue != null)
{
BindingMetadata returnParameterBindingMetadata = GetBindingMetadata(ScriptConstants.SystemReturnParameterBindingName, scriptInvocationContext);
if (returnParameterBindingMetadata != null)
{
scriptInvocationResult.Return = GetBindingValue(returnParameterBindingMetadata.DataType, httpScriptInvocationResult.ReturnValue);
}
// This is additional codes for Durable Function of custom handler
else
{
scriptInvocationResult.Return = GetBindingValue(DataType.String, httpScriptInvocationResult.ReturnValue);
}
}
```

#### Describe alternatives you've considered
n/a

#### Additional context
n/a

Start with src/WebJobs.Script.Grpc/Channel/GrpcWorkerChannel.cs and src/WebJobs.Script/Workers/Http/HttpScriptInvocationResultExtensions.cs, following the linked sections that process orchestrator and custom-handler return values. Compare the built-in worker path with the $return binding check, then determine and verify the intended behavior when that binding is absent.

Written by the indexing model from the issue text.