Some fixes to paradropping (#6609)

# About the pull request
You cannot get hit by stray bullets, get lit on fire, trigger traps and
many more while mid-air.

# Explain why it's good for the game
Makes more sense this way.

# Testing Photographs and Procedure
<details>
I commented out clearing the chute, then tried to shoot past my
character, flame my character and teleport my character on top of a
resin trap. Flaming still does damage without igniting, but let's assume
it's the heat.

<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
balance: being mid-paradrop won't trigger traps, fire and stray bullets
before you land.
/:cl:

code/__DEFINES/dcs/signals/atom/signals_movable.dm

@@ -11,6 +11,9 @@
 	#define COMPONENT_CANCEL_MOVE (1<<0)
 /// From /turf/open/gm/river/Entered(): (turf/open/gm/river/river, covered)
 #define COMSIG_MOVABLE_ENTERED_RIVER "movable_entered_river"
+/// From /atom/movable/proc/doMove: I think it only works with forceMove so watch out
+#define COMSIG_MOVABLE_FORCEMOVE_PRE_CROSSED "movable_forcemove_pre_crossed"
+	#define COMPONENT_IGNORE_CROSS (1<<0)
 
 ///from /mob/living/carbon/xenomorph/start_pulling(): (mob/living/carbon/xenomorph/X)
 #define COMSIG_MOVABLE_XENO_START_PULLING "movable_xeno_start_pulling"

code/__DEFINES/traits.dm

@@ -161,6 +161,8 @@
 #define TRAIT_MERGED_WITH_WEEDS "merged_with_weeds"
 /// Apply this to identify a mob as temporarily muted
 #define TRAIT_TEMPORARILY_MUTED "temporarily_muted"
+/// Mob wont get hit by stray projectiles
+#define TRAIT_NO_STRAY "trait_no_stray"
 
 // SPECIES TRAITS
 /// Knowledge of Yautja technology

code/game/objects/structures/stool_bed_chair_nest/xeno_nest.dm

@@ -245,6 +245,7 @@
 
 	do_buckle(mob, user)
 	ADD_TRAIT(mob, TRAIT_NESTED, TRAIT_SOURCE_BUCKLE)
+	ADD_TRAIT(mob, TRAIT_NO_STRAY, TRAIT_SOURCE_BUCKLE)
 	SEND_SIGNAL(mob, COMSIG_MOB_NESTED, user)
 
 	if(!human)
@@ -275,6 +276,7 @@
 	buckled_mob.pixel_y = 0
 	buckled_mob.old_y = 0
 	REMOVE_TRAIT(buckled_mob, TRAIT_NESTED, TRAIT_SOURCE_BUCKLE)
+	REMOVE_TRAIT(buckled_mob, TRAIT_NO_STRAY, TRAIT_SOURCE_BUCKLE)
 	var/mob/living/carbon/human/buckled_human = buckled_mob
 
 	var/mob/dead/observer/G = ghost_of_buckled_mob

code/game/turfs/transit.dm

@@ -138,6 +138,12 @@
 	clear_active_explosives()
 	ADD_TRAIT(src, TRAIT_IMMOBILIZED, TRAIT_SOURCE_DROPSHIP_INTERACTION)
 	ADD_TRAIT(src, TRAIT_UNDENSE, TRAIT_SOURCE_DROPSHIP_INTERACTION)
+	ADD_TRAIT(src, TRAIT_NO_STRAY, TRAIT_SOURCE_DROPSHIP_INTERACTION)
+	RegisterSignal(src, COMSIG_MOVABLE_FORCEMOVE_PRE_CROSSED, PROC_REF(cancel_cross))
+	RegisterSignal(src, list(
+		COMSIG_LIVING_FLAMER_FLAMED,
+		COMSIG_LIVING_PREIGNITION
+	), PROC_REF(cancel_fire))
 	var/image/cables = image('icons/obj/structures/droppod_32x64.dmi', src, "chute_cables_static")
 	overlays += cables
 	var/image/chute = image('icons/obj/structures/droppod_64x64.dmi', src, "chute_static")
@@ -163,8 +169,18 @@
 		return
 	REMOVE_TRAIT(src, TRAIT_IMMOBILIZED, TRAIT_SOURCE_DROPSHIP_INTERACTION)
 	REMOVE_TRAIT(src, TRAIT_UNDENSE, TRAIT_SOURCE_DROPSHIP_INTERACTION)
+	REMOVE_TRAIT(src, TRAIT_NO_STRAY, TRAIT_SOURCE_DROPSHIP_INTERACTION)
+	UnregisterSignal(src, list(
+		COMSIG_MOVABLE_FORCEMOVE_PRE_CROSSED,
+		COMSIG_LIVING_FLAMER_FLAMED,
+		COMSIG_LIVING_PREIGNITION
+	))
 	overlays -= cables
 	overlays -= chute
+	for(var/atom/movable/atom in loc)
+		if(atom == src)
+			continue
+		atom.Cross(src)
 
 /atom/movable/proc/clear_active_explosives()
 	for(var/obj/item/explosive/explosive in contents)
@@ -232,6 +248,13 @@
 		death(last_damage_data)
 	status_flags |= PERMANENTLY_DEAD
 
+/atom/movable/proc/cancel_cross()
+	SIGNAL_HANDLER
+	return COMPONENT_IGNORE_CROSS
+
+/atom/movable/proc/cancel_fire()
+	SIGNAL_HANDLER
+	return COMPONENT_NO_BURN
 
 /turf/open/space/transit/dropship/alamo
 	shuttle_tag = DROPSHIP_ALAMO

code/modules/movement/movement.dm

@@ -140,11 +140,11 @@
 			destination.Entered(src, oldloc)
 			if(destarea && (old_area != destarea || !isturf(oldloc)))
 				destarea.Entered(src, oldloc)
-
-			for(var/atom/movable/AM in destination)
-				if(AM == src)
-					continue
-				AM.Crossed(src, oldloc)
+			if(!(SEND_SIGNAL(src, COMSIG_MOVABLE_FORCEMOVE_PRE_CROSSED) & COMPONENT_IGNORE_CROSS))
+				for(var/atom/movable/AM in destination)
+					if(AM == src)
+						continue
+					AM.Crossed(src, oldloc)
 
 		Moved(oldloc, NONE, TRUE)
 		. = TRUE

code/modules/projectiles/projectile.dm

@@ -841,8 +841,8 @@
 //mobs use get_projectile_hit_chance instead of get_projectile_hit_boolean
 
 /mob/living/proc/get_projectile_hit_chance(obj/projectile/P)
-	if((body_position == LYING_DOWN || HAS_TRAIT(src, TRAIT_NESTED)) && src != P.original)
-		return FALSE // Snowflake check for xeno nests, because we want bullets to fly through even though they're standing in it
+	if((body_position == LYING_DOWN || HAS_TRAIT(src, TRAIT_NO_STRAY)) && src != P.original)
+		return FALSE
 	var/ammo_flags = P.ammo.flags_ammo_behavior | P.projectile_override_flags
 	if(ammo_flags & AMMO_XENO)
 		if((status_flags & XENO_HOST) && HAS_TRAIT(src, TRAIT_NESTED))