Validate ShaderPrototype IDs (#38728)

* Convert all shader prototype string literals to protoids in overlays

* Convert more shader prototype literal strings to protoids

* Convert ValidatePrototypeId to ProtoId

* Later

Content.Client/Movement/Systems/FloorOcclusionSystem.cs

@@ -8,6 +8,8 @@ namespace Content.Client.Movement.Systems;
 
 public sealed class FloorOcclusionSystem : SharedFloorOcclusionSystem
 {
+    private static readonly ProtoId<ShaderPrototype> HorizontalCut = "HorizontalCut";
+
     [Dependency] private readonly IPrototypeManager _proto = default!;
 
     private EntityQuery<SpriteComponent> _spriteQuery;
@@ -48,7 +50,7 @@ public sealed class FloorOcclusionSystem : SharedFloorOcclusionSystem
         if (!_spriteQuery.Resolve(sprite.Owner, ref sprite.Comp, false))
             return;
 
-        var shader = _proto.Index<ShaderPrototype>("HorizontalCut").Instance();
+        var shader = _proto.Index(HorizontalCut).Instance();
 
         if (sprite.Comp.PostShader is not null && sprite.Comp.PostShader != shader)
             return;