By scaling the pixbuf when loading, existing assets can be used.

When drawing the workspace switcher OSD, we want it to be slightly
transparent to match the OSD style. Also changed how the popup size is
calculated and changed window icons to cairo surfaces.

Instead of converting from surface to a GdkPixbuf and then back to
a surface, we keep it as a surface for the entire manipulation flow.
This improves rendering speed a bit and sets the ground for a higher
resolution thumbnail in the future.

When loading window control buttons and icon as pixbufs, we just set
them as the source for the cairo context used to paint them. Instead, we
now convert them to cairo surfaces and scale them to the correct display
density before painting them.

This allows us to load higher resolution assets (i.e. at twice the size)
and by explicitly setting the intended size in the theme draw_ops, we
can then scale them down to fit lower resolution displays, or render
them at full density for HiDPI displays.

ui/tabpopup.c:176:7: warning: format not a string literal, argument types not checked [-Wformat-nonliteral]
  176 |       tmp = g_markup_printf_escaped (formatter, str);
      |       ^~~

finally, apps that prefer dark theme variant (gtk-application-prefer-dark-theme
in GtkSettings) should also have dark window decorations

taken from:
https://github.com/GNOME/metacity/commit/6b0d325442b995a78b8783384f7ec370db1369a4

- this will be needed for proper window decoration color updates on theme change
  when theme variants fixes are applied

- realize/unrealize functions are dropped instead of map/unmap ones, because
  we didn't change these during GTK+3 porting

- MetaFrames now has GtkWindow as parent instead of GtkInvisible, otherwise
  the hack doesn't work (revert part of 96c7256d638b8c76c8abf786ba307e82a595dd67)

adapted from:
https://github.com/GNOME/metacity/commit/ba8500663457ad9f18ebfdf405162c2cb5caf88f

and make variable names less similar

taken from:
https://github.com/linuxmint/muffin/commit/6120bddefd709d3f1