Change classes that use FieldLoader to use read-only collections.

OpenRA.Mods.Common/Traits/Conditions/GrantConditionOnPrerequisite.cs

@@ -9,6 +9,7 @@
  */
 #endregion
 
+using System.Collections.Immutable;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -23,7 +24,7 @@ namespace OpenRA.Mods.Common.Traits
 
 		[FieldLoader.Require]
 		[Desc("List of required prerequisites.")]
-		public readonly string[] Prerequisites = [];
+		public readonly ImmutableArray<string> Prerequisites = [];
 
 		public override object Create(ActorInitializer init) { return new GrantConditionOnPrerequisite(this); }
 	}