Error line/column returned by DeprecationsHaveAReason is not exact

[cjoudrey]

At the moment the DeprecationsHaveAReason rule will use the line and column of the FieldDefinition node rather than the affected @directive node.

This means if someone were to highlight the error it would lead to highlighting the wrong part of the line.

Example

Current:

11:3 The field `user.firstName` is deprecated but has no deprecation reason.

  firstName: String @deprecated
  ^^^^^^^^^

What we actually want:

11:21 The field `user.firstName` is deprecated but has no deprecation reason.

  firstName: String @deprecated
                    ^^^^^^^^^^^