"Hide file tree browser" tooltip should only show on hover

Context

When users open the file tree browser, the Hide file tree browser tooltip is shown every single time. This is both annoying, and an odd user experience, as users expect tooltips to appear on hover. Having a tooltip appear on open of the file tree also adds unnecessary visual clutter to GitLab's information-dense UI.

Design proposal

The Hide file tree browser tooltip should only appear on hover of the file tree browser button when the file tree browser is open: