view-switcher-button: Make an active button's label bold

This makes the view switcher easier to read.

It uses multiple labels with or without the specific style rather than a
single label with the style toggled on and off to ensure the size
requests don't change depending on whether the button is active or not.
7 jobs for view-switcher-bold in 8 minutes and 9 seconds (queued for 2 seconds)