Support value param for radios

[frankieroberto]

Currently, if you want to support pre-selecting the right option when going back to a radio field (eg from check your answers), you have to do this:

{{ radios({
  "idPrefix": "example",
  "name": "example",
  "fieldset": {
    "legend": {
      "text": "Are you 18 or over?",
      "classes": "nhsuk-fieldset__legend--l",
      "isPageHeading": true
    }
  },
  "items": [
    {
      "value": "yes",
      "text": "Yes",
      checked: (data.example == "yes")
    },
    {
      "value": "no",
      "text": "No",
      checked: (data.example == "no")
    }
  ]
}) }}

This can be quite long-winded if there are a lot of options.

It’d be easier if we could support a top-level value option which sets the current value (if set), and then checks the right radio option:

{{ radios({
  "idPrefix": "example",
  "name": "example",
  "value": data.example,
  "fieldset": {
    "legend": {
      "text": "Are you 18 or over?",
      "classes": "nhsuk-fieldset__legend--l",
      "isPageHeading": true
    }
  },
  "items": [
    {
      "value": "yes",
      "text": "Yes"
    },
    {
      "value": "no",
      "text": "No"
    }
  ]
}) }}

See code in GOVU.UK Design System for radios