docs(cdk/stepper): change misleading documentation (#23377)
docs(cdk/stepper): change misleading documentation (#23377)

The "Accessibility' section of the stepper docs was talking about the stepper having built-in accessibility treatment, even though it doesn't have any, because we don't have control over the component's markup.

These changes reword the section to make it more accurate.

Fixes #23044.
josephperrott/material2,josephperrott/material2,angular/components,angular/components,crisbeto/material2,crisbeto/material2,crisbeto/material2,josephperrott/material2,crisbeto/material2,josephperrott/material2,angular/components,josephperrott/material2,angular/components