Fix UIColor handling per theme (#1995)

UIColor sheet has color sets per theme. Updated `UIColorWidget` to
reflect that, and added `SeStringDrawParams.ThemeIndex` to let users
choose which theme color set to use while drawing SeString from Dalamud.

Dalamud/Interface/Internal/Windows/Data/DataWindow.cs

@@ -56,7 +56,7 @@ internal class DataWindow : Window, IDisposable
         new TaskSchedulerWidget(),
         new TexWidget(),
         new ToastWidget(),
-        new UIColorWidget(),
+        new UiColorWidget(),
     };
 
     private readonly IOrderedEnumerable<IDataWindowWidget> orderedModules;