Menu Button Examples: Change focus indicator to use outline

[mcking65]

In the three menu button examples, per suggestion from @DavidMacDonald in issue #384, change the focus ring to use outline  rather than border.

1. Navigation menu button
2. Actions Menu Button Example Using element.focus()
3. Action Menu Button Example Using aria-activedescendant

[mcking65]

@DavidMacDonald, you wrote in issue #384:

You can prevent the page from jiggling as the user tabs by using outline rather than border for the focus ring

The task force has discussed considerations for using both outline and border for the custom focus rings. There are good reasons for either approach. It is possible to use border without any "jiggling" issues. If border is used and elements do get pushed around, we would definitely consider that a bug.

We do not observe any jiggling issues in the 3 menu button examples that use border. If we have overlooked something, please re-open this issue and let us know.

BTW, in issue #590, we plan to offer some guidance on this topic.