Convert Breadcrumb to be a SDC

[djcelaya]

See #5405.

Summary

Convert the az_barrio breadcrumb override into a Single Directory Component.

This change extracts the breadcrumb markup into a new theme component and keeps the existing breadcrumb template as a thin presenter that includes the component. The goal is to make breadcrumb the first low-risk SDC proof of concept in az_barrio without changing its rendered output or preprocess behavior.

Changes

• Add a new breadcrumb SDC in the az_barrio theme
• Refactor the breadcrumb Twig override to include the new component
• Keep existing breadcrumb preprocess logic unchanged
• Extend the az_barrio functional test to verify breadcrumb visibility and markup behavior

Why breadcrumb first

Breadcrumb is a good first SDC candidate because it is already isolated in a single Twig override, has a simple data contract, and does not require JS or component-specific library work. This lets us validate theme-level SDC usage with minimal behavioral risk.

Testing

• lando phpunit --filter AzBarrioTest

Notes

• This change does not alter the existing breadcrumb preprocess contract
• This change does not reorganize theme libraries
• This is intended as an initial SDC proof of concept for az_barrio