fix(material/stepper): swap aria-roles from tab to more generic ones

[adolgachev]

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Deployed dev-app for 7aef232 to: https://ng-dev-previews-comp--pr-angular-components-31785-dev-cjba0uxx.web.app

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[github-actions]

Deployed docs-preview for 3a52715 to: https://ng-dev-previews-comp--pr-angular-components-31785-docs-tknoutb8.web.app

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[adolgachev]

This breaks too much in google3 and also loses a lot on the accessibility front when just a group.

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