Import gitlab-ui component and typescale scales last

What does this MR do?

Try to resolve !30619 (closed)

Import bootstrap first, then framework, then gitlab-ui component styles.

There are still some issues here, e.g .btn.gl-link is now blue (link colored) whereas it used to be black (because .btn was defined later).

This also means we are basically duplicating gitlab_ui.scss and are strongly coupled to gitlab-ui's SCSS structure (though this is already the case).