Website code links should use <a> tag, not <button>

[slorber]

The code tab has many UX problems, one of them is not using <a> tags for links (breadcrumb + displayed code tree).

This makes it impossible to use middle/wheel-click to open a file in a new tab.

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Probably related to the fact that the opened file is not persisted in querystring so it's not possible to deep-link to a given file (issue npm/feedback#946)

All this makes it super unconvenient and time-consuming to browse multiple files at once: we must open multiple tabs from the code tree root, and navigate them one by one to the desired file.