Refactor resource hints into entities

Follow-up to ✨ Refactor resource hints into entities Closed: won't fix

Problem/Motivation

Resource hints are currently stored as a delimited string in the variables system. Per "pending functionality" in the project description, resource hints require individual configuration to support the crossorigin and as attributes for comprehensive support of all resource hints requirements/features.

Proposed resolution

Pivot to a new resource hint entity type and leverage the entity facilities to manage configurations for a resource hint in an individual basis, and refactor any/all current functionality as necessary.

Remaining tasks

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User interface changes

Yes. Entity CRUD using the base entity management forms available in the entity ecosystem.

API changes

N/A. See ✨ Module hook to alter resource hint array Active

Data model changes

Yes. New resource hints entity.