Content switcher: Usage tab

[laurenmrice]

Ref original issue: https://github.com/carbon-design-system/carbon-website/issues/3364 Ref Usage tab PDF comments: https://ibm.ent.box.com/file/1000659943858?s=t9lhd31mvvga5ks3xu49xb0opnha5vv4

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Usage tab updates

Icon content switcher: Add content and images to sections that apply. Anatomy: Consider specifying the region area below the switcher. Sizing > Width section: Look at a11y comment in PDF. Content > Text label section: Include information on truncation behavior. Behaviors: Should we add references to selectionmode: automatic versus default or is that too dev specific? Consult with a dev on the team. States: Refine how we want to display states here. Usually now we are showing a table on the Usage tab describing the states, rather than showing images. Also add focus states. Interactions: Remove Screenreader section.