docs-bug(Accessibility): Clarifying Accessibility target in documentation

### Documentation Feedback

I'm evaluating component libraries to use in an enterprise app, and accessibility is a key consideration. Having looked through the documentation, I'm not able to find a specific target for Angular Material's accessibility. Would you all consider specifying which WCAG level you are targeting? PrimeNG specifically calls out that they meet the WCAG 2.1 AA standard. While Angular Material seems to put a lot of work into accessibility, it would be helpful to be able to state that the component library we use targets a specific WCAG level.

### Affected documentation page

material.angular.io

Open material.angular.io and review the existing accessibility guidance to find where the library's target is described or missing. Confirm the intended WCAG level with maintainers, then document that target on the relevant page; done means users can clearly identify the stated accessibility target.

Written by the indexing model from the issue text.