fix(ui5-list): suppress F2 aria description when no interactive items present

[NakataCode]

Problem

When the List has selectionMode="None" and contains only plain standard items, the screen reader incorrectly announces "To move to the content, press F2" via aria-description on the <ul> element.

This affects the Tokenizer in read-only mode, which sets selectionMode="None" on its internal List in the n-more popover, causing the misleading instruction to be announced even though there are no interactive elements to reach with F2.

---

Solution

Introduce a _hasInteractiveItems getter that gates the F2 instruction, returning true only when any of the following conditions are met:

• selectionMode is Delete — the custom delete button slot may be tabbable
• Any item has type="Detail" — the detail button is tabbable
• Any item is a ListItemCustom — arbitrary tabbable slot content

---

Important Note:

• The F2 aria-description is now only announced when the list actually contains interactive elements that can be reached with F2. Previously it was announced on every list regardless of content.

Fixes: #13347

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13489--ui5-webcomponents-preview.netlify.app

[dobrinyonkov]

item.hasAttribute("ui5-li-custom") only matches the literal <ui5-li-custom> tag. The [ui5-li-custom] marker attribute is set by UI5Element from the component's own tag (see packages/base/src/UI5Element.ts:335 — setAttribute(getPureTag(), "")), so a subclass like class MySpecialItem extends ListItemCustom registered as <my-special-item> will carry [my-special-item] but not [ui5-li-custom]. Consumers extending ListItemCustom will lose the F2 announcement on this PR.

Per packages/base/AGENTS.md ("No instanceof Checks"), the project's idiom for subclass-safe identity is createInstanceChecker with a duck-typing marker — already used by MenuItem, MenuItemGroup, MultiComboBoxItemGroup, etc.

Suggested approach:

// In ListItemCustom.ts
class ListItemCustom extends ListItemBase {
    readonly isCustomListItem = true;
}
export const isInstanceOfListItemCustom = createInstanceChecker<ListItemCustom>("isCustomListItem");

// In List.ts
import { isInstanceOfListItemCustom } from "./ListItemCustom.js";

get _hasInteractiveItems() {
    if (this.selectionMode === ListSelectionMode.Delete) {
        return true;
    }
    return this.getItems().some(item => {
        return item.type === "Detail" || isInstanceOfListItemCustom(item);
    });
}

Note: getAttribute("type") itself is fine — UI5Element reflects property writes back to the attribute (UI5Element.ts:729-734). But reading item.type directly is cleaner and matches the surrounding style.

[dobrinyonkov]

Worth calling out in the PR description / release notes: this change silently removes the F2 aria-description from any default <ui5-list> (no selectionMode, plain standard items). That's the intended fix, but consumers who relied on that announcement on a default list will lose it without a deprecation path. The test edit here is the visible signal of that behavior change.