Merge branch 'fix-dnd-coordinates-on-windows' into 'master'

Fix DND coordinates on Windows

See merge request GNOME/gtk!3930

diff --cc gdk/win32/gdkdrag-win32.c
Simple merge

diff --cc gdk/win32/gdkdrop-win32.c
Simple merge

diff --cc gdk/win32/gdksurface-win32.c
Simple merge