Add radiators (#18728)

* Add radiators

* Limit heat transfer to fluid heat capacity

* Adjust datafield names

* Fix material arbitrage

* This code has been debugged, and so there are no more bugs. Debugging code is therefore unnecessary

* Adjust radiator layer subfloor visibility

* Cache CVars

* No default

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

* Like and unsubscribe

* Fix CVar caching

---------

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Resources/Textures/Structures/Piping/Atmospherics/heatexchanger.rsi/meta.json

@@ -0,0 +1,19 @@
+{
+   "version":1,
+   "size":{
+      "x":32,
+      "y":32
+   },
+   "license":"CC-BY-SA-3.0",
+   "copyright":"Taken from https://github.com/tgstation/tgstation at commit 57cd1d59ca019dd0e7811ac451f295f818e573da and modified by BasedUser",
+   "states":[
+      {
+         "name":"heStraight",
+         "directions":4
+      },
+      {
+         "name":"heBend",
+         "directions":4
+      }
+   ]
+}