New rule: Summary element has non-empty accessible name

[WilcoFiers]

New rule to test that summary elements have an accessible name.

I don't think this is covered by any other rule today, since summary elements do not have a semantic role.

Need for Call for Review: 2 weeks

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[tombrunet]

An inapplicable example for two summary elements to catch the third applicability bullet would be useful.

[Jym77]

I like it 👍

Needs another review

Couple tweaks, please have another look

Changes done.

[giacomo-petri]

In Firefox, the ::marker CSS pseudo-element is part of the accessibility tree, which means the accessible name cannot be left empty in Firefox.

Should we address this, clarifying that the "triangle" icon is not enough?

[carlosapaduarte]

Why would the element having a semantic role of button make it fail this rule? Is this copy/paste from another rule?

[carlosapaduarte]

Add failed example with two summary elements, being the first empty