Add system for loading extra serializer strings.

"fixture-0" comes up a LOT so we load this manually now.

Robust.Server/BaseServer.cs

@@ -371,6 +371,19 @@ namespace Robust.Server
                 var reg = factory.GetRegistration(regType);
                 _stringSerializer.AddString(reg.Name);
             }
+
+            using var extraMappedStrings = typeof(BaseServer).Assembly
+                .GetManifestResourceStream("Robust.Server.ExtraMappedSerializerStrings.txt");
+
+            if (extraMappedStrings != null)
+            {
+                using var sr = new StreamReader(extraMappedStrings);
+                string? line;
+                while ((line = sr.ReadLine()) != null)
+                {
+                    _stringSerializer.AddString(line);
+                }
+            }
         }
 
         private bool SetupLoki()

Robust.Server/ExtraMappedSerializerStrings.txt

@@ -0,0 +1 @@
+fixture-0

Robust.Server/Robust.Server.csproj

@@ -29,6 +29,9 @@
     <Content Include="server_config.toml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <EmbeddedResource Include="ExtraMappedSerializerStrings.txt">
+      <LogicalName>Robust.Server.ExtraMappedSerializerStrings.txt</LogicalName>
+    </EmbeddedResource>
   </ItemGroup>
   <Import Project="..\MSBuild\Robust.Engine.targets" />
 </Project>