Update TSCN file format documentation for Godot 4.0

[Calinou]

• Related to setget doesn't exist in 4.0 and isnt part of GDScript Grammar #6265.

Your Godot version: 4.0.rc1

Issue description: TSCN file format documentation is outdated:

• Numeric resource IDs were replaced by string UUIDs.
• Extraneous spaces around parentheses are no longer present and should be removed from the examples.
• ArrayMesh and Animaion formats are likely outdated due to backwards-incompatible changes in Godot 4.
• The page should be renamed to "TSCN and TRES file formats", as it effectively covers both formats.

URL to the documentation page: https://docs.godotengine.org/en/latest/contributing/development/file_formats/tscn.html

[Calinou]

I've started working on this: https://github.com/Calinou/godot-docs/tree/update-tscn-file-format