arch/sim: fix X11 framebuffer window not visible in POSIX simulator

The X11 framebuffer implementation in the POSIX simulator was creating a window
and graphics context but failing to map (display) the window to thescreen with XMapWindow().

This omission meant the framebuffer window would be created in the X11server but remain hidden,
making it impossible to see any graphics outputfrom the simulator. The window existed in the X11
server's state but wasnot rendered to the screen.

This fix adds the missing XMapWindow(display, g_window) call aftercreating the graphics context, which:
1. Maps the created X11 window to the screen (makes it visible).
2. Ensures framebuffer output is rendered to the display as expected.
3. Maintains compatibility with existing X11 framebuffer logic.

The change restores basic visibility of the simulator's framebuffer window,
fixing a critical usability issue for graphics-related testing in the POSIX simulator.

Signed-off-by: chao an <anchao.archer@bytedance.com>

arch/sim/src/sim/posix/sim_x11framebuffer.c

@@ -166,6 +166,11 @@ static inline Display *sim_x11createframe(void)
   gcval.graphics_exposures = 0;
   g_gc = XCreateGC(display, g_window, GCGraphicsExposures, &gcval);
 
+  /* Map the window to make it visible on the display after it has been
+   * created and configured
+   */
+
+  XMapWindow(display, g_window);
   return display;
 }