Content switcher: Usage tab

[laurenmrice]

Ref original issue: #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.