[Complex Text Layouts] Refactor Font class, default themes and controls to use Text Server interface.

Implement interface mirroring.
Add TextLine and TextParagraph classes.
Handle UTF-16 input on macOS and Windows.

scene/scene_string_names.h

@@ -130,6 +130,7 @@ public:
 	StringName _update_xform;
 
 	StringName _clips_input;
+	StringName _structured_text_parser;
 
 	StringName _proxgroup_add;
 	StringName _proxgroup_remove;