Provide names and pools when creating MiniYaml.

- Rename the filename parameter to name and make it mandatory. Review all callers and ensure a useful string is provided as input, to ensure sufficient context is included for logging and debugging. This can be a filename, url, or any arbitrary text so include whatever context seems reasonable.
- When several MiniYamls are created that have similar content, provide a shared string pool. This allows strings that are common between all the yaml to be shared, reducing long term memory usage. We also change the pool from a dictionary to a set. Originally a Dictionary had to be used so we could call TryGetValue to get a reference to the pooled string. Now that more recent versions of dotnet provide a TryGetValue on HashSet, we can use a set directly without the memory wasted by having to store both keys and values in a dictionary.

OpenRA.Mods.Common/UpdateRules/Rules/20230225/ExplicitSequenceFilenames.cs

@@ -37,7 +37,8 @@ namespace OpenRA.Mods.Common.UpdateRules.Rules
 		{
 			// Keep a resolved copy of the sequences so we can account for values imported through inheritance or Defaults.
 			// This will be modified during processing, so take a deep copy to avoid side-effects on other update rules.
-			this.resolvedImagesNodes = MiniYaml.FromString(resolvedImagesNodes.WriteToString()).ConvertAll(n => new MiniYamlNodeBuilder(n));
+			this.resolvedImagesNodes = MiniYaml.FromString(resolvedImagesNodes.WriteToString(), nameof(BeforeUpdateSequences))
+				.ConvertAll(n => new MiniYamlNodeBuilder(n));
 
 			var requiredMetadata = new HashSet<string>();
 			foreach (var imageNode in resolvedImagesNodes)
@@ -285,7 +286,7 @@ namespace OpenRA.Mods.Common.UpdateRules.Rules
 						imageNode.Value.Nodes.Insert(inheritsNodeIndex, defaultsNode);
 					}
 
-					var nodes = MiniYaml.FromString(duplicateTilesetCount.First(kv => kv.Value == maxDuplicateTilesetCount).Key);
+					var nodes = MiniYaml.FromString(duplicateTilesetCount.First(kv => kv.Value == maxDuplicateTilesetCount).Key, nameof(UpdateSequenceNode));
 					defaultTilesetFilenamesNode = new MiniYamlNodeBuilder("TilesetFilenames", "", nodes);
 					defaultsNode.Value.Nodes.Insert(0, defaultTilesetFilenamesNode);
 				}