[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/gui/link_button.h

@@ -33,6 +33,7 @@
 
 #include "scene/gui/base_button.h"
 #include "scene/resources/bit_map.h"
+#include "scene/resources/text_line.h"
 
 class LinkButton : public BaseButton {
 	GDCLASS(LinkButton, BaseButton);
@@ -46,17 +47,46 @@ public:
 
 private:
 	String text;
+	Ref<TextLine> text_buf;
 	UnderlineMode underline_mode;
 
+	Dictionary opentype_features;
+	String language;
+	TextDirection text_direction = TEXT_DIRECTION_AUTO;
+	Control::StructuredTextParser st_parser = STRUCTURED_TEXT_DEFAULT;
+	Array st_args;
+
+	void _shape();
+
 protected:
 	virtual Size2 get_minimum_size() const override;
 	void _notification(int p_what);
 	static void _bind_methods();
 
+	bool _set(const StringName &p_name, const Variant &p_value);
+	bool _get(const StringName &p_name, Variant &r_ret) const;
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
 public:
 	void set_text(const String &p_text);
 	String get_text() const;
 
+	void set_structured_text_bidi_override(Control::StructuredTextParser p_parser);
+	Control::StructuredTextParser get_structured_text_bidi_override() const;
+
+	void set_structured_text_bidi_override_options(Array p_args);
+	Array get_structured_text_bidi_override_options() const;
+
+	void set_text_direction(TextDirection p_text_direction);
+	TextDirection get_text_direction() const;
+
+	void set_opentype_feature(const String &p_name, int p_value);
+	int get_opentype_feature(const String &p_name) const;
+	void clear_opentype_features();
+
+	void set_language(const String &p_language);
+	String get_language() const;
+
 	void set_underline_mode(UnderlineMode p_underline_mode);
 	UnderlineMode get_underline_mode() const;