[Design] Improve repository navigation - path and find file
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Based on the feedback from GitLab team members https://gitlab.com/gitlab-org/gitlab/-/issues/452146, here is an opportunity to improve the top area of the directory and file layout so that the repository navigation with the secondary breadcrumb and actions are clear.

From https://gitlab.com/gitlab-org/gitlab/-/issues/452146#note_1833475409
> It isn't clear to me what the :mag: button will search. It could be for a file, within this file, or for a branch. How are you imagining people will use it?
From https://gitlab.com/gitlab-org/gitlab/-/issues/452146#note_1834151738
> Another idea that would help traverse files would be to make the path elements dropdowns rather than nav links, allowing users to browse within that directory similar to various IDEs
From https://gitlab.com/gitlab-org/gitlab/-/issues/450660#note_1836929262
> Ah, I don't know if I would think the magnifying glass is what I would look for...
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