Migrate default export to named export(s) in src/directives/safe_link/safe_link.js

• Convert the default export to named export(s) in src/directives/safe_link/safe_link.js.
• Make sure that internal import statements are also updated to reflect this change.
  • WARNING: some of the default exports might be used outside of GitLab UI. Use your best judgement to determine when a given export might be used in consuming projects. Those cases should be flagged as breaking changes and should be submitted along with integration MRs in the projects we control.
• Remove the override from .eslintrc.yml.
• Put an MR up, and integration MRs if needed.
• Follow the standard review process.