Extracts magic strings from Tag calls (#36305)

* Extracts magic strings from Tag calls

When #36281 gets merged, the `TagSystem` methods will all give warnings. Let's fix those warnings before they even happen!

* Adds missing libraries

* Remove not yet implemented TagSystem changes

* Fix tag spelling error

Genuinely surprised there was only 1!

* Styling and proper type changes

* Styling

Co-authored-by: Tayrtahn <tayrtahn@gmail.com>

---------

Co-authored-by: Tayrtahn <tayrtahn@gmail.com>

Content.Server/Zombies/ZombieSystem.Transform.cs

@@ -36,6 +36,7 @@ using Content.Shared.Traits.Assorted;
 using Robust.Shared.Audio.Systems;
 using Content.Shared.Ghost.Roles.Components;
 using Content.Shared.Tag;
+using Robust.Shared.Prototypes;
 
 namespace Content.Server.Zombies;
 
@@ -61,6 +62,8 @@ public sealed partial class ZombieSystem
     [Dependency] private readonly TagSystem _tag = default!;
     [Dependency] private readonly NameModifierSystem _nameMod = default!;
 
+    private static readonly ProtoId<TagPrototype> InvalidForGlobalSpawnSpellTag = "InvalidForGlobalSpawnSpell";
+
     /// <summary>
     /// Handles an entity turning into a zombie when they die or go into crit
     /// </summary>
@@ -290,6 +293,6 @@ public sealed partial class ZombieSystem
 
         //Need to prevent them from getting an item, they have no hands.
         // Also prevents them from becoming a Survivor. They're undead.
-        _tag.AddTag(target, "InvalidForGlobalSpawnSpell");
+        _tag.AddTag(target, InvalidForGlobalSpawnSpellTag);
     }
 }