[Feature Request] Allow response files to resolve the environment variables.

When using environment variables in command line, OS resolve these environment variables.
**Example:**
```
# Windows
--token %token%

# Linux
--token $token
```

When trying to use the response file, the Environment Variables are not resolved and used as is.
Currently, System.Command enables the use of the ``` [env:key=value] ``` directive, allowing environment variables to be set from the command line during invocation.
Also, it support of resolving nesting response files for tokens prefixed by ``` @.```

It is nice if System.Command-line-api can support resolving the Environment Variables in response file based on OS .