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

OpenRA.Mods.Common/Traits/DeliversCash.cs

@@ -10,6 +10,7 @@
 #endregion
 
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using OpenRA.Mods.Common.Activities;
 using OpenRA.Mods.Common.Orders;
 using OpenRA.Primitives;
@@ -30,7 +31,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string Type = null;
 
 		[Desc("Sound to play when delivering cash")]
-		public readonly string[] Sounds = [];
+		public readonly ImmutableArray<string> Sounds = [];
 
 		[CursorReference]
 		[Desc("Cursor to display when hovering over a valid actor to deliver cash to.")]