Add collapsible behavior to term edit page

[gabrielcld2]

Approach

• Refactored taxonomies.js to support multiple collapsible instances per page using querySelectorAll, resolving content targets via a data-collapsible-target attribute and getElementById. Visibility is now toggled via
  the hidden attribute (replacing style.display) to correctly handle both <div> and <tbody> elements. Arrow icon state uses classList.toggle with a force argument.
• Added aria-expanded, aria-controls, and aria-label to all collapsible toggle buttons for screen reader accessibility.
• Extracted the card box-model styles from .cloudinary-collapsible into a --card BEM modifier in _settings.scss, keeping layout-specific styles separate from the shared toggle/content rules. Extended the __toggle
  heading selector to cover both h2 and h3.
• Updated taxonomy-transformation-fields.php to use the --card modifier, wire up data-collapsible-target / id on the toggle and content elements, and replace style="display:none" with the hidden attribute.
• Added collapsible behavior to taxonomy-term-transformation-fields.php using paired <tbody> elements per transformation context — a toggle row containing the heading and button, and a content <tbody> (initially
  hidden) wrapping the existing field rows — preserving valid table structure throughout.
• Added custom CSS class cloudinary-term-transformations to the tbody elements added by Cloudinary so that it can be targeted for custom styling if needed.

QA notes

• Go to the taxonomy term edit form
  • Confirm the custom cloudinary fields are now shown behind a dropdown
  • You should be able to toggle the dropdown to see its content
• Confirm the the taxonomy term creation form still shows the dropdown as before