Pass entity through AJAX request

Problem/Motivation

A selection handler cannot see the entity being edited. Excluding the entity from its own suggestions, or narrowing the matches by something on the entity, has nothing to work from: the selection settings the autocomplete route receives carry no entity.

Steps to reproduce

1. Put a break in a selection handler while the Autocomplete Deluxe widget is configured.
2. Type in the field and look at the selection settings.

Proposed resolution

Send the entity type and id with the autocomplete request, and load the entity into the selection settings on the controller, only when it loads and the user may view it. The element also carries the entity in its selection settings, so validation sees it too. The hashed settings and the key value store keep leaving the entity out, so one field keeps one key.

Remaining tasks

• ✅ File an issue
• ✅ Addition/Change/Update/Fix
• ✅ Testing to ensure no regression
• ➖ Automated unit testing coverage
• ➖ Automated functional testing coverage
• ➖ UX/UI designer responsibilities
• ➖ Readability
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• ➖ Performance
• ✅ Security
• ➖ Developer Documentation
• ➖ User Guide Documentation
• ➖ Reviewed by human
• ➖ Code review by maintainers
• ➖ Full testing and approval
• ➖ Credit contributors
• ➖ Review with the product owner
• ➖ Release notes snippet
• ❌ Release

User interface changes

• N/A

API changes

• A selection handler receives the entity being edited in its settings under entity, when there is one.

Data model changes

• N/A

Release notes snippet

• Selection handlers receive the entity being edited, so a handler can leave the entity out of its own suggestions.