Add support for statbar “off state” icons (#9462)

This adds support for optional “off state” icons for statbars. “off state icons” can be used to denote the lack of something, like missing hearts or bubbles.

Add "off state" textures to the builtin statbars.

Co-authored-by: SmallJoker <mk939@ymail.com>

src/hud.cpp

@@ -46,6 +46,7 @@ const struct EnumString es_HudElementStat[] =
 	{HUD_STAT_WORLD_POS, "world_pos"},
 	{HUD_STAT_SIZE,    "size"},
 	{HUD_STAT_Z_INDEX, "z_index"},
+	{HUD_STAT_TEXT2,   "text2"},
 	{0, NULL},
 };