[GTK] Option to auto hide titlebar

[ak1932]

Give an option to auto hide the titlebar in gtk after a few seconds if cursor is not on it. Bring back the title bar once the cursor comes near it.
This reduces the clutter as well as give users window decorations for resizing the window.
The terminal Blackbox https://gitlab.gnome.org/raggesilver/blackbox does this pretty well and the only reason I used to use it.
This is different from the discussion which states to only hide titlebar in fullscreen as this would give a cleaner look all the time

[mitchellh]

Just a warning to anyone that Blackbox is GPL so we can't look at the source to see how they do this.

[ak1932]

As I see it, this can be done in gtk using the Revealer widget. By wrapping the header bar in a revealer widget and tracking the mouse movement to trigger it. I am willing to work on this if someone could direct me in the places I'd have to change.

[pluiedev]

I like this idea in principle, but we'd have to think about whether to make the tab bar then an overlay or a regular bar in the toolbar view. The latter option is simpler to implement but it forces a resize and throws everything off (especially bad for non-floating WMs), where as an overlay is visually cleaner but requires more code.

(P.S. You don't need to add a Revealer for ToolbarView bars. They already have one. See https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/method.ToolbarView.set_reveal_top_bars.html)