Expose hotkeys to localisation.

Allows the Settings > Hotkeys screen to be localised, including hotkey decriptions, groups and contexts.

The hotkey names are exposed to localisation via KeycodeExts. Hotkey modifiers are similarly exposed via ModifersExts.

The Settings > Input screen has a Zoom Modifier dropdown, which shows the localised modifier name.

The --check-yaml utility command is taught to recognise all hotkey translation, so it can validate their usage.

OpenRA.Mods.Common/UtilityCommands/ExtractYamlStrings.cs

@@ -43,7 +43,7 @@ namespace OpenRA.Mods.Common.UtilityCommands
 				.Where(t => t.Name.EndsWith("Info", StringComparison.InvariantCulture) && t.IsSubclassOf(typeof(TraitInfo)))
 				.ToDictionary(
 					t => t.Name[..^4],
-					t => t.GetFields().Where(f => f.HasAttribute<FluentReferenceAttribute>()).Select(f => f.Name).ToArray())
+					t => Utility.GetFields(t).Where(Utility.HasAttribute<FluentReferenceAttribute>).Select(f => f.Name).ToArray())
 				.Where(t => t.Value.Length > 0)
 				.ToDictionary(t => t.Key, t => t.Value);