made evac signs glow (#38545)

Co-authored-by: Ed <96445749+TheShuEd@users.noreply.github.com>

Resources/Prototypes/Entities/Structures/Wallmounts/Signs/signs.yml

@@ -104,7 +104,15 @@
   description: A direction sign, pointing out which way evac is.
   components:
   - type: Sprite
-    state: direction_evac
+    layers:
+    - state: direction_evac
+    - state: direction_evac_glow
+      shader: unshaded
+    - state: direction_evac_glow
+      shader: shaded
+      #This is a neat trick I found to sort of "hack" an emissive map into ss14. Basically, the direction_evac_glow texture has an alpha channel.
+      #Alpha doesn't work for unshaded, but for *shaded* it does, and by putting a shaded texture infront of the unshaded, we can dim the unshaded texture, effectively allowing brightness control.
+      #I am re-using this from my high-vis vest PR, where I go further into detail, https://github.com/space-wizards/space-station-14/pull/37869
 
 - type: entity
   parent: BaseSignDirectional

Resources/Textures/Structures/Wallmounts/signs.rsi/meta.json

@@ -5,7 +5,7 @@
         "y": 32
     },
     "license": "CC-BY-SA-3.0",
-    "copyright": "Taken from https://github.com/discordia-space/CEV-Eris at commit 4e0bbe682d0a00192d24708fdb7031008aa03f18 and bee station at commit https://github.com/BeeStation/BeeStation-Hornet/commit/13dd5ac712385642574138f6d7b30eea7c2fab9c, Job signs by EmoGarbage404 (github) with inspiration from yogstation and tgstation, 'direction_exam' and 'direction_icu' made by rosieposieeee (github), 'direction_atmos' made by SlamBamActionman, 'vox' based on sprites taken from vgstation13 at https://github.com/vgstation-coders/vgstation13/blob/e7f005f8b8d3f7d89cbee3b87f76c23f9e951c27/icons/obj/decals.dmi, 'direction_pods' derived by WarPigeon from existing directional signs., 'detective' derived by Soupkilove from existing security sign",
+    "copyright": "Taken from https://github.com/discordia-space/CEV-Eris at commit 4e0bbe682d0a00192d24708fdb7031008aa03f18 and bee station at commit https://github.com/BeeStation/BeeStation-Hornet/commit/13dd5ac712385642574138f6d7b30eea7c2fab9c, Job signs by EmoGarbage404 (github) with inspiration from yogstation and tgstation, 'direction_exam' and 'direction_icu' made by rosieposieeee (github), 'direction_atmos' made by SlamBamActionman, 'vox' based on sprites taken from vgstation13 at https://github.com/vgstation-coders/vgstation13/blob/e7f005f8b8d3f7d89cbee3b87f76c23f9e951c27/icons/obj/decals.dmi, 'direction_pods' derived by WarPigeon from existing directional signs., 'detective' derived by Soupkilove from existing security sign, direction_evac_glow made by moomoobeef based on existing direction_evac",
     "states": [
         {
             "name": "ai"
@@ -165,6 +165,10 @@
             "name": "direction_evac",
             "directions": 4
         },
+        {
+            "name": "direction_evac_glow",
+            "directions": 4
+        },
         {
             "name": "direction_supply",
             "directions": 4