Add @text_view_bg to the theme colors, fixes gnome-terminal

When gnome-terminal tries to get the system colors, it will fail to get the newish "@text_view_bg" color and fall back to (0,0,0,0). However the terminal itself doesn't mark the background as being transparent so you get graphical glitches. See: https://gitlab.gnome.org/GNOME/vte/-/issues/284

By adding "@text_view_bg" to the breeze theme, gnome-terminal now gets a valid color and the program renders correctly.

Signed-off-by: Sebastian Parborg sebastian@blender.org