nested-interactive incorrectly triggering when using role="dialog"

[luketheobscure]

The following code triggers the nested-interactive rule:

<div role="dialog">
  <button>foo</button>
</div>

This is a common pattern when using modal dialogs.

[nathanhammond]

For notes:

1. Any time we have role="dialog" it should probably have a tabindex: <div role="dialog" tabindex="-1">
2. role="dialog" is allowed to have interactive child elements. Probably worth treating it as inert rather than interactive.

[rwjblue]

/cc @martndemus

[rwjblue]

dialog is listed as part of the standard widget roles (from https://www.w3.org/TR/wai-aria/complete#widget_roles). I can certainly remove dialog from the list of interactive ARIA roles, but I'd really like to have some sort of backup/reasoning on why some of those roles are considered interactive and others aren't.