Add full-path loader

What does this MR do?

This MR refactors some of our GraphQL infrastructure, adding a new full-path loader outside of the resolver/mutations hierarchy, and avoiding resolver re-use. This is re-used by !31227 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

/label ~backstage