Resolve "Add dropdown panel tips pointing at the toggle"

What does this MR do?

Add indicator arrow to dropdown menu.

• The indicator should calculate the correct alignment to the toggle using floating-ui's arrow middleware.
• If the toggle is wider than the menu, the indicator will be positioned 24px inset on the side nearest the toggle's center.
• To accommodate the indicator's 4px height, the menu has been shifted 4px away from the toggle. Unfortunately, this will break any visual tests that use an open dropdown.

Screenshots or screen recordings

Integration merge requests

• GitLab: gitlab!175571
• CustomersDot: mr_url
• Status Page: mr_url

Does this MR meet the acceptance criteria?

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Conformity

• Code review guidelines.
• GitLab UI's contributing guidelines.
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• 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

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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.

Closes #2180