A11y: ToC Block links are not marked as ToC links

[Tishasoumya-02]

Problem: Every ToC-Link are not labeled as such. Whenever a screenreader is used, it doesn't tell the user that the link is a ToC-Link. The link seems to be linking to another page, but that is not the case. It's always an anchor link. This might confuse the user.

Proposed Solution: Mark the links as table-of-contents-links with alt-tags or ARIA-labels. A screenreader should read "Title-of-the-link, table-of-content-link" or something similar.

Steps to reproduce:

• Create Table-of-Contents block in page and populate it.
• Inspect Table-of-Contents-Links or use a screenreader
• Link is not shown as ToC-Link, no aria label, no alt tag

Expected result:

• The link should be marked as Table-of-Contents-Link

WCAG - 2.1:

• https://www.w3.org/TR/WCAG21/#label-in-name

BIK BITV-Test (Web):

• 9.2.5.3: https://ergebnis.bitvtest.de/pruefschritt/bitv-20-web/bitv-20-web-9-2-5-3-sichtbare-beschriftung-teil-des-zugaenglichen-namens

[ichim-david]

I left a review on the pull request https://github.com/plone/volto/pull/6084#pullrequestreview-2105250544 From my point of view this proposed solution does more harm than good and although we can improve the toc accesibility by ensuring we have good markup this solution will not improve the accessibility but decrease it.