Fixes blood emissives rendering below disposals pipes and other floor objects (#94024)

## About The Pull Request

So KEEP_APART with a set plane has a fun behavior where topdown objects
still keep their topdown layer, which causes FLOAT_LAYER emissives on
floor objects to render above everything else. This includes emissive
blockers, and I have missed static blockers in my original PR so here
they are.

Fixes this.

<img width="222" height="116" alt="image"
src="https://github.com/user-attachments/assets/5762864c-f732-4196-81b7-9cee415f1af8"
/>


## Changelog
🆑
fix: Fixed blood emissives rendering below disposals pipes and other
floor objects
/🆑

code/__DEFINES/layers.dm

@@ -159,6 +159,9 @@
 // NOTICE: we break from the pattern of increasing in steps of like 0.01 here
 // Because TOPDOWN_LAYER is 10000 and that's enough to floating point our modifications away
 
+/// Used to shift all topdown layer emissives to a the game plane equivalent layers, as otherwise they render above everything else due to being KEEP_APART
+#define TOPDOWN_TO_EMISSIVE_LAYER(layer) LERP(FLOOR_EMISSIVE_START_LAYER, FLOOR_EMISSIVE_END_LAYER, (layer - (TOPDOWN_LAYER + 1)) / TOPDOWN_LAYER_COUNT)
+
 // Must be equal to the offset of the highest topdown layer
 #define TOPDOWN_LAYER_COUNT 18
 

code/__HELPERS/lighting.dm

@@ -1,5 +1,3 @@
-#define TOPDOWN_TO_EMISSIVE_LAYER(layer) LERP(FLOOR_EMISSIVE_START_LAYER, FLOOR_EMISSIVE_END_LAYER, (layer - (TOPDOWN_LAYER + 1)) / TOPDOWN_LAYER_COUNT)
-
 /// Produces a mutable appearance glued to the [EMISSIVE_PLANE] dyed to be the [EMISSIVE_COLOR].
 /proc/emissive_appearance(icon, icon_state = "", atom/offset_spokesman, layer, alpha = 255, appearance_flags = NONE, offset_const, effect_type = EMISSIVE_BLOOM)
 	if((isnull(layer) || layer == FLOAT_LAYER) && IS_TOPDOWN_PLANE(offset_spokesman.plane))
@@ -99,5 +97,3 @@
 	var/atom/movable/vis_cast = make_blocker
 	vis_cast.vis_contents += hand_back
 	return hand_back
-
-#undef TOPDOWN_TO_EMISSIVE_LAYER

code/game/atoms_movable.dm

@@ -174,6 +174,8 @@
 		blocker.dir = dir
 		blocker.appearance_flags = appearance_flags | EMISSIVE_APPEARANCE_FLAGS
 		blocker.plane = GET_NEW_PLANE(EMISSIVE_PLANE, PLANE_TO_OFFSET(plane)) // Takes a light path through the normal macro for a microop
+		if (IS_TOPDOWN_PLANE(plane))
+			blocker.layer = TOPDOWN_TO_EMISSIVE_LAYER(layer)
 		// Ok so this is really cursed, but I want to set with this blocker cheaply while
 		// Still allowing it to be removed from the overlays list later
 		// So I'm gonna flatten it, then insert the flattened overlay into overlays AND the managed overlays list, directly