More overflow:hidden and rounded frames
This merge request has following changes:
GTK_OVERFLOW_HIDDENin some container widgets to not draw children outside of them.
Make frames rounded in Adwaita as per GNOME mockups.Partially moved to !2476 (merged).
Minimal fixes to avoid double borders in some demos and inspector. (They are also intended to make the rounded frames look not-so-bad... but in any case double borders are ugly.)Moved to !2478 (merged) & !2477 (merged).
Example of the rounded frames:
Related issue: #3012 (closed)
CC @jimmac for the style change.