Make GNOME Builder more adaptive

[rangelovd (Denis Rangelov)]

Following this issue on gitlab (stating the reason GNOME Builder can’t be used as a code editor on mobile devices is that it can’t fit on small screen) I decided to make a concept that squeezes GNOME Builder window. Unfortunately it has a big min-w and for a good reason - elements are not fitting into the screen. hence some proposals.

1. Move Search to the top left side of the paneldockchild
2. Move Hamburger menu to top right side of paneldockchild if the panel is presented, if it’s hidden let it stay on the right side of the headerbar as it is now
3. Make paneldockchild act as Adw.OverlaySplitView
4. Hide tabs on small screens if there is only one tab
5. Make plus with arrow button "New Tab’ icon because that’s what it actually does though with extra steps
6. Hide some unnecessary information on small screens from statusbar until requested
7. Decrease minimal width

I think that would be a good start

[chergert (Christian Hergert)]

This will be extremely difficult, but if someone manages to make it work we can take a look. It will likely require an ABI break and complete redesign of libpanel to do right.