Create helper service for Social mention module

[Ressinel]

It is good to have a helper service to be possible to use mentions functions where needed.

Problem

There is not possible to reuse some mentions functionality. E.g. get prefix and suffix.

Solution

Add a helper service with appropriate methods.

Issue tracker

• https://www.drupal.org/project/social/issues/3307272

Theme issue tracker

N/A

How to test

• [ ] No functionality changed

Definition of done

Before merge

• [ ] Code/peer review is completed
• [ ] All commit messages are clear and clean. If applicable a rebase was performed
• [ ] All automated tests are green
• [ ] Functional/manual tests of the acceptance criteria are approved
• [ ] All acceptance criteria were met
• [ ] New features or changes to existing features are covered by tests, either unit (preferably) or behat
• [ ] Update path is tested. New hook_updates should respect update order, right naming convention and consider hook_post_update code
• [ ] Module can be safely uninstalled. Update/implement hook_uninstall and make sure that removed configuration or dependencies are removed/uninstalled
• [ ] This pull request has all required labels (team/type/priority)
• [ ] This pull request has a milestone
• [ ] This pull request has an assignee (if applicable)
• [ ] Any front end changes are tested on all major browsers
• [ ] New UI elements, or changes on UI elements are approved by the design team
• [ ] New features, or feature changes are approved by the product owner

After merge

• [ ] Code is tested on all branches that it has been cherry-picked
• [ ] Update hook number might need adjustment, make sure they have the correct order
• [ ] The Drupal.org ticket(s) are updated according to this pull request status

Screenshots

N/A

Release notes

N/A

Change Record

N/A

Translations

N/A

[mergeable[bot]]

Thanks for contributing towards Open Social! A maintainer from the @goalgorilla/maintainers group might not review all changes from all teams/contributors. Please don't be discouraged if it takes a while. In the meantime, we have some automated checks running and it might be that you will see our comments with some tips or requests to speed up the review process. :blush:

[open-social-tugboat]

Tugboat has finished building the preview for this pull request!

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Dashboard:

• https://dashboard.tugboatqa.com/62ea367f19770b441a511988

[tbsiqueira]

Cherry-picked to 11.5.x here c9bddff5e1294ce154c2d739c92f9abfb6138a8b