Resolve "Move segmented_control_button_group from main GitLab project to GitLab UI"

What does this MR do?

Closes #1787 (closed)

More context: #2821 (comment 2173307530)

In this MR, I move GitLab's segmented_control_button_group.vue to GitLab UI. I did minor adaptions in the spec file to make it work within the GitLab/UI setup and to make it work within Vue 3.

I did not create a new component, but replaced the deprecated GlSegmentControl with the new implementation. Although I'd have prefered Radio Buttons over a Button Group, schematically. But this is another discussion. I created two integration branches, one to update the usage within GitLab, and one to remove the deprecated status in design.gitlab.com (see Integration merge requests below). Before I made sure that GlSegmentedControl was not used in GitLab anymore: gitlab!170594 (merged).

The component automatically inherit design tokens from the GlButtonGroup and GlButton and comes completely without its own CSS.

Screenshots or screen recordings

Integration merge requests

• GitLab: gitlab!171080 (merged)
• Pajamas Design: gitlab-org/gitlab-services/design.gitlab.com!4151 (merged)

Does this MR meet the acceptance criteria?

This checklist encourages the authors, reviewers, and maintainers of merge requests (MRs) to confirm changes were analyzed for conformity with the project's guidelines, security and accessibility.

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Conformity

• Code review guidelines.
• GitLab UI's contributing guidelines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened (see integration merge requests above).
• Added the ~"component:*" label(s) if applicable.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• Security reports checked/validated by a reviewer from the AppSec team

Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.