the "change scenes manually" page should be moved to after the "using SceneTree" page

[val461]

Your Godot version: 4.6

Issue description:
These 2 pages (mentioned in the title of this issue) in the "Core features" chapter are in a confusing order in my opinion.

Indeed, the "change scenes manually" page:

• mentions autoloads (introduced in a later page)
• says "Sometimes it helps to have more control over how you swap scenes around"
  • which feels like it belongs after the "Changing current scene" paragraph of the "using SceneTree" page.

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/stable/tutorials/scripting/change_scenes_manually.html
https://docs.godotengine.org/en/stable/tutorials/scripting/scene_tree.html
https://docs.godotengine.org/en/stable/tutorials/scripting/index.html#core-features