Trim memory usage of IReadOnlyPackage implementations.

These implementations are often backed by a Dictionary, and tend to live a long time after being loaded. Ensure TrimExcess is called on the backing dictionaries to reduce the long term memory usage. In some cases, we can also preallocate the dictionary size for efficiency.

OpenRA.Mods.Common/FileSystem/InstallShieldPackage.cs

@@ -37,7 +37,7 @@ namespace OpenRA.Mods.Common.FileSystem
 			public string Name { get; }
 			public IEnumerable<string> Contents => index.Keys;
 
-			readonly Dictionary<string, Entry> index = new();
+			readonly Dictionary<string, Entry> index;
 			readonly Stream s;
 			readonly long dataStart = 255;
 
@@ -63,7 +63,8 @@ namespace OpenRA.Mods.Common.FileSystem
 					s.Position = tocAddress;
 
 					// Parse directories
-					var directories = new Dictionary<string, uint>();
+					var directories = new Dictionary<string, uint>(dirCount);
+					var totalFileCount = 0;
 					for (var i = 0; i < dirCount; i++)
 					{
 						// Parse directory header
@@ -75,12 +76,16 @@ namespace OpenRA.Mods.Common.FileSystem
 						// Skip to the end of the chunk
 						s.Position += chunkSize - nameLength - 6;
 						directories.Add(dirName, fileCount);
+						totalFileCount += fileCount;
 					}
 
 					// Parse files
+					index = new Dictionary<string, Entry>(totalFileCount);
 					foreach (var dir in directories)
 						for (var i = 0; i < dir.Value; i++)
 							ParseFile(dir.Key);
+
+					index.TrimExcess();
 				}
 				catch
 				{