docs(material/stepper): updates docs to use new aria roles

Updates previous documentation so it uses the correct/updated aria roles of
, , and  with the
attribute.

Author: essjay05

src/cdk/stepper/stepper.md

@@ -59,10 +59,10 @@ resetting it will call `reset` on the underlying form control which clears the v
 
 ### Accessibility
 Apart from the built-in keyboard support, the stepper doesn't apply any treatment. When implementing
-your own component, it is recommended that the stepper is treated as a tabbed view for accessibility
-purposes by giving it a `role="tablist"`. The header of step that can be clicked to select the step
-should be given `role="tab"`, and the content that can be expanded upon selection should be given
-`role="tabpanel"`. Furthermore, the step header should have an `aria-selected` attribute that
-reflects its selected state.
+your own component, it is recommended that the stepper is treated as a grouped view for accessibility
+purposes by giving it a `role="group"`. The header of step that can be clicked to select the step
+should be given `role="button"`, and the content that can be expanded upon selection should be given
+`role="region"`. Furthermore, the step header should have an `aria-expanded` attribute that
+reflects its expanded state.
 
 You can refer to the [Angular Material stepper](https://github.com/angular/components/tree/main/src/material/stepper) as an example of an accessible implementation.

src/material/stepper/stepper.md

@@ -228,10 +228,10 @@ export class MyApp {}
 <!-- example(stepper-intl) -->
 
 ### Accessibility
-The stepper is treated as a tabbed view for accessibility purposes, so it is given
-`role="tablist"` by default. The header of step that can be clicked to select the step
-is given `role="tab"`, and the content that can be expanded upon selection is given
-`role="tabpanel"`. `aria-selected` attribute of step header is automatically set based on
+The stepper is treated as a grouped view for general accessibility purposes, so it is given
+`role="group"` by default. The header of step that can be clicked to select the step
+is given `role="button"`, and the content that can be expanded upon selection is given
+`role="region"`. `aria-expanded` attribute of step header is automatically set based on
 step selection change.
 
 The stepper and each step should be given a meaningful label via `aria-label` or `aria-labelledby`.