Fix module ancestor check for imports

[jjcnn]

Description

When importing items we allow imports from ancestor modules, even if the ancestor module is declared as private.

The code that performs this check was moved from module.rs to root.rs as part of #5697. During this move the current module path (i.e., the path of the destination of the import) was mistakenly replaced with the module path of the root module of the destination module. Since root modules do not have ancestors this meant that no source module was ever considered an ancestor of the destination module.

This PR fixes this problem, and adds an abscure test case that shows the issue.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[codspeed-hq]

CodSpeed Performance Report

Merging #6671 will not alter performance

_{Comparing jjcnn/fix-import-ancestor-check (db441a7) with master (cc842e3)}

Summary

✅ 22 untouched benchmarks