Documentation generation for GDScript

- ClassDoc added to GDScript and property reflection data were extracted
from parse tree

- GDScript comments are collected from tokenizer for documentation and
applied to the ClassDoc by the GDScript compiler

- private docs were excluded (name with underscore prefix and doesn't
have any doc comments)

- default values (of non exported vars), arguments are extraced from the
parser

- Integrated with GDScript 2.0 and new enums were added.

- merge conflicts fixed

editor/plugins/script_editor_plugin.h

@@ -482,6 +482,7 @@ public:
 	void close_builtin_scripts_from_scene(const String &p_scene);
 
 	void goto_help(const String &p_desc) { _help_class_goto(p_desc); }
+	void update_doc(const String &p_name);
 
 	bool can_take_away_focus() const;