fix(ui5-dynamic-page): validate aria-controls reference before rendering

[NakataCode]

Problem:

• Invalid ARIA attributes were being generated when the referenced header element wasn't available with the exact ID.

Solution:

• Remove _accAttributesForHeaderActions because the header and the (pin/unpin/expand/collapse) actions exist in separate shadow DOMs.

Fixes: #10987

[dobrinyonkov]

The aria-controls attribute only functions within the same shadow DOM scope. In this case, the header and the (pin/unpin/expand/collapse) actions exist in separate shadow DOMs. This is why the AXE tool initially reported an error—it couldn't locate the header element within the shadow DOM of the actions.

There is ongoing development in this area, and the ElementInternals.ariaControlsElements API (still a work in progress) may eventually provide a solution. Unfortunately, until it's fully supported, we can't improve the situation. I recommend removing the aria-controls-related code for now and revisiting it once the new API becomes available.

Note: this.querySelector returns null because it searches in the "light" DOM, where the custom element, slots, and other elements are defined. To query within the Shadow DOM, you need to use this.shadowRoot!.querySelector, which will locate the header once the component is rendered. However, despite this, the error mentioned above still occurs.