[Lens] Chart type switcher in single layer is not usable with keyboard

[wylieconlon]

I was looking through recently reported accessibility issues and realized that these icons appear to have keyboard focus disabled:

While there is an alternative way to switch the entire chart to a specific chart type, there is no way to do this with the keyboard only. This is related to, but not directly the same as, this other issue:

#79923

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

@wylieconlon If you select the button group you can switch around the individual items using arrow left and arrow right.

In this video I'm pressing arrow right, then arrow left: