core+platforms, revise pico pen handling

the MSB in the tablet position register denotes pen on surface.
add logic and a hotkey for handling pen not on surface. This allows
for repositioning of the pen without the storyware reacting to it.

platform/common/menu_pico.c

@@ -362,7 +362,8 @@ me_bind_action emuctrl_actions[] =
 	{ "Pico Next page   ", PEV_PICO_PNEXT },
 	{ "Pico Prev page   ", PEV_PICO_PPREV },
 	{ "Pico Switch input", PEV_PICO_SWINP },
-	{ "Pico Display pen ", PEV_PICO_PEN },
+	{ "Pico Pen sensor  ", PEV_PICO_PPOSV },
+	{ "Pico Show pen    ", PEV_PICO_SHPEN },
 	{ NULL,                0 }
 };