Close #24104 This also introduces many tests to cover many complex error handling functions. ### Before The details are never shown in production. <details>  </details> ### After The details could be shown to site admin users. It is safe.  |
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| alert.tmpl | ||
| alert_details.tmpl | ||
| delete_modal_actions.tmpl | ||
| disable_form_autofill.tmpl | ||
| footer.tmpl | ||
| footer_content.tmpl | ||
| head.tmpl | ||
| head_navbar.tmpl | ||
| head_script.tmpl | ||
| paginate.tmpl | ||