[Issue] reference directive restored for _extends.less. extends replaced to mixins in _extend.less

[m2-assistant]

This issue is automatically created based on existing pull request: #35101: reference directive restored for _extends.less. extends replaced to mixins in _extend.less

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Description (*)

When I installed a clear M2, I saw that the reference directive removed for the import of _extends.less file. I've found this PR and I explained why removing reference is a bad idea:
#31793 (comment)

I've investigated later how to restore reference but repair the issue of Grunt in the PR.

And I've found a solution described here:
#31793 (comment)

@ihor-sviziev asked me to create a PR with the fix, so I made it.

Related Pull Requests

#31793

Manual testing scenarios (*)

1. Create a new theme which extends Magento Blank theme.
2. Compile styles via default deploying (setup:static-content:deploy) and via Grunt.
3. Look at block titles of My Account (they should look the same after all build processes).
4. Find matches of abs selectors in styles-m.css and styles-l.css files. Quantity of them and the size of styles-m.css should be less in comparison with the main branch (2.4-develop).

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[github-jira-sync-bot]

✅ Jira issue https://jira.corp.adobe.com/browse/AC-8024 is successfully created for this GitHub issue.

[m2-assistant]

✅ Confirmed by @engcom-Lima. Thank you for verifying the issue.
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