positional (unnamed) arguments

In my experience there are many cases where it is beneficial to be able to have a directive with a single unnamed argument:

```graphql
@import("some import specification") instead of @import(defs: "some import specification")
@default("some default value") instead of @default(value: "some default value")
@calculated("some expression") instead of @calculated(expression: "some expression")
```

There are multiple ways this could be allowed ranging from a general concept of positional arguments to a narrow special case for directives with a single argument.

### Questions

1. Has positional arguments been discussed before?
2. Does anyone else have use cases that would benefit from positional arguments?