Add vtable slots: icon_select, icon_change_title, clip_icon_paint,
drawer_icon_paint, balloon_init, do_kaboom, menu_paint_entry,
menu_draw_frame.
Replace policy call sites with vtable dispatch. Make paintEntry and
drawFrame in menu.c non-static as wMenuPaintEntry/wMenuDrawFrame.
X11 backend calls the mechanism functions; Wayland backend is no-op.
wFrameWindowPaint now only reached through X11 backend's frame_paint.
Levi Neely
Levi Neely