[avatar-group] Consider using roving tabindex

[web-padawan]

Currently, if there are many avatars, it might be hard to tab past the avatar group.
One of the participants suggested to use the same tabbing approach as in vaadin-tabs.

[knoobie]

Please take a look at https://www.w3.org/TR/wai-aria-practices/#keyboard combined with https://www.w3.org/TR/wai-aria-practices/#toolbar. Using the arrow keys to navigate inside the avatar group sounds like a good trade of.

And example of a working toolbar can be found here as well: https://www.w3.org/TR/wai-aria-practices/examples/toolbar/toolbar.html

[web-padawan]

@knoobie thank you for your input. It looks like using roving tabindex for the vaadin-avatar-group would make sense 👍