2acc8d01bcdcceffc2ca85ca537f01dc3b118a78  AX: setting AXSelected on an option does not do what the user interface of the select does

Classified as not security-relevant.
Triage note: Removes per-subclass AccessibilityListBoxOption/AccessibilityMenuListOption::setSelected and adds a single AccessibilityNodeObject::setSelected plus HTMLOptionElement::setSelectedByUser (which checks isActuallyDisabled/multiple); a11y refactor with minor guard logic, no memory-safety bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+4.87), area:Source/WebCore/html (+2.0)