Use aria-hidden for decorative SVG images

[aduth]

🛠 Summary of changes

Updates decorative SVG images to use aria-hidden instead of role="img".

This builds upon #10200, and seeks to address the original issue while avoiding some incompatibilities between the role and expectations around decorative images.

This is partly motivated by errors surfaced by automated checking tools, e.g. Axe's aria-allowed-role or PageSpeed Insights.

Some background investigation leading to this:

• Originally spotted a recommendation in a blog post by a well-known accessibility engineer, not directly related to this issue, though similarly recommending aria-hidden for decoratives images
• More authoritatively through specifications:
  • role="presentation" has an intended use-case for decorative images: "An element whose content is completely presentational (like a [...] decorative graphic"
  • However, the original bug persists with this implementation
  • Further into the description for this role is the following: "Consequently, using role="presentation" or role="none" on an HTML img is equivalent to using aria-hidden="true"."
  • Using aria-hidden addresses the original bug

📜 Testing Plan

Repeat testing plan from #10200

Optionally, run a scan using an accessibility tool like Axe to verify there are no errors.