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/Lint/CheckTranslationReference.cs

@@ -148,7 +148,7 @@ namespace OpenRA.Mods.Common.Lint
 
 			foreach (var filename in modData.Manifest.ChromeLayout)
 			{
-				var nodes = MiniYaml.FromStream(modData.DefaultFileSystem.Open(filename));
+				var nodes = MiniYaml.FromStream(modData.DefaultFileSystem.Open(filename), filename);
 				foreach (var node in nodes)
 					CheckChrome(node, translation, Language, emitError, emitWarning, translatableFields);
 			}