[v4] Rendering of checkboxes and radios changed

[GBH]

Right now I see:

<div class="form-check">
  <label class="form-check-label" for="user_misc_1">
    <input class="form-check-input" type="checkbox" value="1" name="user[misc][]" id="user_misc_1" />
    Foo
  </label>
</div>

<div class="radio">
  <label for="user_misc_1">
    <input type="radio" value="1" name="user[misc]" id="user_misc_1" />
    Foo
  </label>
</div>

Where it should be:

<div class="form-check">
  <input class="form-check-input" type="checkbox" value="" id="defaultCheck1">
  <label class="form-check-label" for="defaultCheck1">
    Default checkbox
  </label>
</div>

<div class="form-check">
  <input class="form-check-input" type="radio" name="exampleRadios" id="exampleRadios1" value="option1" checked>
  <label class="form-check-label" for="exampleRadios1">
    Default radio
  </label>
</div>

See: https://getbootstrap.com/docs/4.0/components/forms/#default-stacked

[mattbrictson]

Good find. Definitely a bug we need to fix for 4.0.0.

[lcreid]

@jeffblake mentioned this in a comment on #361. It's good to track this in its own issue.

[lcreid]

Should custom radio buttons be rendered the same as before:

      <div class="custom-control custom-radio">
        <input class="custom-control-input" id="user_misc_1" name="user[misc]" type="radio" value="1" />
        <label class="custom-control-label" for="user_misc_1">This is a radio button</label>
      </div>

Should custom check boxes be rendered the same as before:

      <div class="custom-control custom-checkbox">
        <input name="user[terms]" type="hidden" value="0" />
        <input class="custom-control-input" id="user_terms" name="user[terms]" type="checkbox" value="1" />
        <label class="custom-control-label" for="user_terms">I agree to the terms</label>
      </div>

[lcreid]

This is what needs to be done for this issue (moved here from PR #407):

• correcting the classes on the radio button elements (Render Bootstrap 4 Radio Buttons and Check Boxes #407 (comment))
• inline radios and checkboxes
• custom controls -- Looks like this was already done. Let me know if you see any discrepancies between our output and the Bootstrap 4 documentation
• update the README where the examples of generated markup are out-of-date
• the "no label" case -- this is really just hide_label and skip_label.

Bonus marks for investigating how accessibility is facilitated for radio buttons and check boxes (e.g. perhaps including an intelligent default for aria-label).