Generalize role=presentation/none unwrapping beyond tables #50

Summary

toSemanticEvents(respectAccessibility = true) currently unwraps role="presentation"/role="none" only for tables (via isLayoutTable()). The same stripping should apply to any element whose role has been neutralised: <ul role="presentation">, <h2 role="none">, <nav role="presentation">, etc. should shed their semantics and promote their children, mirroring the accessibility tree. This is a small generalization of the shipped layout-table code.

Depends on #48 (shared introspection layer + flowElement treatment classifier).

Examples

⚠️ The trap

computedRole == "generic" is ubiquitous — every <div>/<span> reports it. The unwrap rule must therefore key off an explicit presentation/none role, NOT off a generic computed role. A blanket "unwrap when generic" would dissolve the entire document.

Two viable detection signals:

1. The raw attribute: getAttribute("role") in {"presentation", "none"} — explicit, unambiguous, does not require the experimental flag.
2. computedRole reflecting presentation conflict resolution (ARIA spec: a focusable element or one with global ARIA states/properties does NOT actually become presentational). computedRole already accounts for these exceptions, so it is the more correct signal — but it needs the flag.

Recommendation: prefer computedRole (handles the "presentation role is ignored on focusable / aria-labelled elements" edge cases the spec mandates), with the explicit-attribute check as the flag-off fallback. Document which path ran.

Suggested approach

Add an Unwrap case to the #48 classifier for the presentation/none verdict, reusing the structural-promotion machinery already built for tables (flowChildren with the tag dropped). For presentation containers with structural children (a presentation <ul>'s <li>s, a presentation table's rows — already handled), the children's own semantics are also stripped per ARIA "required owned elements" rules; the table code does this via TABLE_STRUCTURAL_TAGS + insideLayoutTable. Generalize that notion so a presentation <ul> likewise strips its <li>s.

Test approach

Deterministic, under ChromeHeadlessExperimentalA11y:

• <ul role="presentation"><li>a</li></ul> → a promoted, no ul/li.
• <h2 role="none">x</h2> → x, no h2.
• Presentation conflict: <button role="presentation">x</button> (focusable) → role is NOT honoured (still a button) — assert it is kept, validating the computedRole path over the naive attribute check.
• Layout-table regression: the existing table tests must still pass.

Out of scope

• Recovering structure from positive roles (that's Recover semantic structure from ARIA roles (div-soup → headings, lists) #49).
• Pruning a11y-ignored nodes (that's Prune accessibility-ignored empty nodes #52) — presentation unwrap keeps the content, pruning removes it entirely; distinct.