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.Game/Manifest.cs

@@ -94,7 +94,8 @@ namespace OpenRA
 			Id = modId;
 			Package = package;
 
-			var nodes = MiniYaml.FromStream(package.GetStream("mod.yaml"), "mod.yaml");
+			var stringPool = new HashSet<string>(); // Reuse common strings in YAML
+			var nodes = MiniYaml.FromStream(package.GetStream("mod.yaml"), $"{package.Name}:mod.yaml", stringPool: stringPool);
 			for (var i = nodes.Count - 1; i >= 0; i--)
 			{
 				if (nodes[i].Key != "Include")
@@ -107,7 +108,7 @@ namespace OpenRA
 					throw new YamlException($"{nodes[i].Location}: File `{filename}` not found.");
 
 				nodes.RemoveAt(i);
-				nodes.InsertRange(i, MiniYaml.FromStream(contents, filename));
+				nodes.InsertRange(i, MiniYaml.FromStream(contents, $"{package.Name}:{filename}", stringPool: stringPool));
 			}
 
 			// Merge inherited overrides