Add support for readonly hotkeys and expose chat input hotkeys

OpenRA.Game/HotkeyManager.cs

@@ -35,7 +35,7 @@ namespace OpenRA
 
 			foreach (var kv in settings)
 			{
-				if (definitions.ContainsKey(kv.Key))
+				if (definitions.ContainsKey(kv.Key) && !definitions[kv.Key].Readonly)
 					keys[kv.Key] = kv.Value;
 			}
 
@@ -61,6 +61,9 @@ namespace OpenRA
 			if (!definitions.TryGetValue(name, out var definition))
 				return;
 
+			if (definition.Readonly)
+				return;
+
 			keys[name] = value;
 			if (value != definition.Default)
 				settings[name] = value;