Suggestion: Improve error message when a function lacks any input bindings

Currently, if any function (method decorated with the `FunctionAttribute`) in the project is missing an input binding, running the project via `func host start` just displays

```A host error has occurred during startup operation '47ee1d6f-61ed-409a-8ce8-f63cb1191a1b'.
Microsoft.Azure.WebJobs.Extensions.FunctionMetadataLoader: At least one binding must be declared.
Failed to stop host instance '670440b8-1a5b-4f4e-bb65-2b4259c769d5'.
Microsoft.Azure.WebJobs.Host: The host has not yet started.
Value cannot be null. (Parameter 'provider')
```

This gives the impression (to me at least) that _no_ bindings were found for any function, rather than an issue with any one specific function.

Could the error message be improved to list the function(s) the error is being thrown for? Something like `Function 'xyz' is missing input bindings. At least one binding must be declared.`

Reproduce the startup failure with `func host start` using a C# method decorated with `FunctionAttribute` but no input binding. Trace the function metadata loading path to identify where the generic error is produced. Done means the startup error identifies each function missing input bindings while retaining the existing binding guidance.

Written by the indexing model from the issue text.