[TODO] Better text alternatives computation for Markdown messages

Feature Request

Fix the TODO inside packages/component/src/Utils/activityAltText.ts:

/** Computes all text from a given HTML document as flattened array. This is best-effort. */
function htmlTextAlternatives(document: Document): string[] {
  // TODO: [P2] #3923 Revisit this logic with W3C standard, we could do a better text alternatives computation.
  //       For example, <abbr title="..."> is not computed.
  //       https://www.w3.org/TR/accname-1.1/#mapping_additional_nd_name
  return walk<HTMLElement>(document, node => {
    const { nodeType, tagName, textContent } = node;

    if (nodeType === Node.TEXT_NODE) {
      return [textContent];
    } else if (tagName === 'IMG') {
      return [node.getAttribute('alt')];
    } else if (!HTML_INLINE_TAGS.includes(tagName)) {
      return ['\n'];
    }
  });
}

[feature-request]

Start in packages/component/src/Utils/activityAltText.ts at htmlTextAlternatives and read the referenced W3C Accessible Name and Description Computation guidance. Compare the current walk logic with the standard, including the noted abbr title example, then use the existing activity text-alternative behavior to verify the computation is improved.