devmode: add devmode_screen cvar, select which splitscreen to display info for

Old behavior was just use the last splitscreen.

This does not the position devmode draws on the screen.

src/d_netcmd.c

@@ -1086,6 +1086,7 @@ void D_RegisterClientCommands(void)
 	COM_AddCommand("weather", Command_Weather_f);
 	COM_AddCommand("grayscale", Command_Grayscale_f);
 	CV_RegisterVar(&cv_renderhitbox);
+	CV_RegisterVar(&cv_devmode_screen);
 
 #ifdef HAVE_DISCORDRPC
 	CV_RegisterVar(&cv_discordrp);

src/m_cheat.c

@@ -694,6 +694,9 @@ struct debugFlagNames_s const debug_flag_names[] =
 	{NULL, 0}
 };
 
+static CV_PossibleValue_t devmode_screen_t[] = {{1, "MIN"}, {4, "MAX"}, {0, NULL}};
+consvar_t cv_devmode_screen = CVAR_INIT ("devmode_screen", "1", CV_CHEAT, devmode_screen_t, NULL);
+
 void Command_Devmode_f(void)
 {
 	size_t argc = 0;

src/m_cheat.h

@@ -89,6 +89,8 @@ void Command_CauseCfail_f(void);
 void Command_Dumplua_f(void);
 #endif
 
+extern consvar_t cv_devmode_screen;
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

src/st_stuff.c

@@ -418,6 +418,9 @@ static void ST_drawDebugInfo(void)
 {
 	INT32 height = 192;
 
+	// devmode_screen = 1..4
+	stplyr = &players[displayplayers[min(r_splitscreen, cv_devmode_screen.value - 1)]];
+
 	if (!stplyr->mo)
 		return;