feat: keep clear-all button in token-selector at top right

What does this MR do?

This MR implements the proposal of #1868 (closed) by:

• Wrapping the tokenContainer and the clear-all button in a seperate flex-container.
• Fixing the alingment when the input wraps. You can notice wierd behavior in the gif in the issue: when the input in the container wraps onto the next row, the space at the top between tokens and container changes.

The implementation requires a defined width for the input field, otherwise the browser assumes a required min-width (for Firefox its around 200px), which results in overflowing the parent container. I've setteled with 40% width of the parent container (gl-w-40p). This behaves like a min-width of the input before flex wraps the input onto a new row. If it's on a new row, the input field grows. Maybe there is a better way of archiving this behavior.(?)

Solves #1868 (closed)

Does this MR meet the acceptance criteria?

Conformity

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• 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
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Accessibility

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• All actions and functionality can be done with a keyboard.
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