Show balloon alert to viewers, no more async (#59256)

Adds balloon_alert_to_viewers, which provides a visible_message-esque interface to show balloon alerts around you. Use sparingly, as I'd also like for Runechat emotes to take this place (such as sneezing not showing in chat, but having an emote).
    balloon_alert no longer yields, letting it be used in SHOULD_NOT_SLEEP(TRUE) procs, like signal handlers.
    Balloon alerts now use get_atom_on_turf(src), meaning if used on mobs they will move with them, rather than on their tile.

code/modules/balloon_alert/balloon_alert.dm

@@ -6,6 +6,29 @@
 
 /// Creates text that will float from the atom upwards to the viewer.
 /atom/proc/balloon_alert(mob/viewer, text)
+	SHOULD_NOT_SLEEP(TRUE)
+
+	INVOKE_ASYNC(src, .proc/balloon_alert_perform, viewer, text)
+
+/// Create balloon alerts (text that floats up) to everything within range.
+/// Will only display to people who can see.
+/atom/proc/balloon_alert_to_viewers(message, self_message, vision_distance = DEFAULT_MESSAGE_RANGE, list/ignored_mobs)
+	SHOULD_NOT_SLEEP(TRUE)
+
+	var/list/hearers = get_hearers_in_view(vision_distance, src)
+	hearers -= ignored_mobs
+
+	for (var/mob/hearer in hearers)
+		if (hearer.is_blind())
+			continue
+
+		balloon_alert(hearer, (hearer == src && self_message) || message)
+
+// Do not use.
+// MeasureText blocks. I have no idea for how long.
+// I would've made the maptext_height update on its own, but I don't know
+// if this would look bad on laggy clients.
+/atom/proc/balloon_alert_perform(mob/viewer, text)
 	var/client/viewer_client = viewer.client
 	if (isnull(viewer_client))
 		return
@@ -15,7 +38,7 @@
 		var/atom/movable/movable_source = src
 		bound_width = movable_source.bound_width
 
-	var/image/balloon_alert = image(loc = loc, layer = ABOVE_MOB_LAYER)
+	var/image/balloon_alert = image(loc = get_atom_on_turf(src), layer = ABOVE_MOB_LAYER)
 	balloon_alert.plane = BALLOON_CHAT_PLANE
 	balloon_alert.alpha = 0
 	balloon_alert.maptext = MAPTEXT("<span style='text-align: center; -dm-text-outline: 1px #0005'>[text]</span>")