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/FileFormats/ReplayMetadata.cs

@@ -48,7 +48,7 @@ namespace OpenRA.FileFormats
 
 			// Read game info (max 100K limit as a safeguard against corrupted files)
 			var data = fs.ReadLengthPrefixedString(Encoding.UTF8, 1024 * 100);
-			GameInfo = GameInformation.Deserialize(data);
+			GameInfo = GameInformation.Deserialize(data, path);
 		}
 
 		public void Write(BinaryWriter writer)