fix(framework): invalidation of unchanged slots

[nnaydenow]

Previously, _updateSlots was called twice — once by a DOM observer monitoring the custom element’s DOM node and once by the slot change event triggered inside shadowRoot.

This update enhances the DOM observer to also monitor the slot attribute of each child within the custom element’s DOM node, eliminating the need for an event listener inside shadowRoot.

Fixes: #10377

[DonkeyCo]

@nnaydenow it seems like TableGrowing.cy is among the tests that are failing for your PR. I've created another PR that solves the issue, you can review it here: #10952