[later phase] Generalize GET/PATCH/DELETE for individual auto-save entries: refactor `ApiConfigAutoSaveControllers` and `ApiAutoSaveController::delete()`

Overview

• ✨ Auto-save code components Active introduced ApiConfigAutoSaveControllers, and restricted it to just code components + asset libraries, and exposes these under /xb/api/v0/config/auto-save/{xb_config_entity_type_id}/{xb_config_entity}, with GET + PATCH
• 📌 For selective reverting add DELETE auto-save endpoint Active added the ::delete() method to ApiAutoSaveController and works for all entities and exposes this under /xb/api/v0/auto-saves/{entity_type}/{entity}' (with obviously only DELETE)

This is inconsistent. We should make it consistent. OTOH, if there's no need for the XB UI to access these, then perhaps it's fine as-is?

Most importantly: GET and PATCH of content entities happens via the /xb/api/v0/layout/{entity_type}/{entity} routes; additional requests would be worse for performance+scalability.

Still, it's possible that in the future we'll want to interact with auto-saves of content entities. Consider this the placeholder issue.

Proposed resolution

User interface changes