[Issue] Add new flexbox mixins

[m2-assistant]

This issue is automatically created based on existing pull request: #30666: Add new flexbox mixins

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Description (*)

This Pr is only improvement add some new flexbox mixins for reuse while developments
So frontenders can reuse it while modify or customise themes

Example when in less arrange layout
we can use .lib-flex-center(); for get flexbox basic styles instead write multiple line like before

Related Pull Requests

Fixed Issues (if relevant)

1. Fixes magento/magento2#<issue_number>

Manual testing scenarios (*)

1. ...
2. ...

Questions or comments

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)
• All automated tests passed successfully (all builds are green)

[m2-assistant]

Hi @engcom-November. Thank you for working on this issue.
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[engcom-November]

Hello @mrtuvn,

Thank you for the report and collaboration!

As you are adding reusable mixins this issue can be marked as feature request.