[PP-1] Integrate UI Icons Menu with Navigation

Postponing until #3516887: Allow to customize Navigation icons → is approved and merged.

Created MR in the meantime to test the integration. To test it locally, it requires to apply the patch from #3516887: Allow to customize Navigation icons → to core first.

Screenshot for reference of the expected usage.

I think this is unblocked now.

Tested with latest version of Core and UI Icons, and everything works as expected.

See evidences:

Thanks for the work and test.
I am not confortable with ignoring the display options of the icon (before/after/no text), neither the fact that it assume that you have a `class` variable in your icon pack, if not we still have the first 2 letters.
I updated with a change to simply add the class to hide the letters in navigation.

Thanks @mogtofu33 for the feedback.

I've been testing the latest changes but it is breaking down the logic, we come back to the current "buggy" state.

I believe Drupal's navigation is a special case and shouldn't be handled the same way as other components. Its structure is unique, and supporting the before/after/no text options could introduce inconsistencies.

Looking at the UI Icons Menu logic, I noticed that the icon is currently wrapped inside <span class="toolbar-button__label">, which doesn't align well with the new navigation requirements. For it to work correctly, the icon should be placed outside this <span>. The previous implementation introduced by @plopesc seems more appropriate here, as this behavior is specific to the Navigation component.

My bad, I didn't properly test the collapse menu.
Thanks again for the review and work, I just added a documentation.