[Read-only inputs]: Toggle implementation

[sstrubberg]

Reference #12241

Acceptance Criteria

• Coded component in /package/react
• Add a prop for read-only, add styles for said prop
• Controls for each state in playground
• Default story for easy copy and paste
• RTL tests for the read-only class on the prop
• When a toggle is readonly and not disabled, the field is read by screenreaders while not allowing the value to be changed.

[laurenmrice]

Just noting here: For the Off read-only state, the text color of the Off label should be $text-primary and not $text-placeholder because it still needs to pass 4.5:1.