Your Godot version:
3.X, 4.0

Issue description:
It's often hard to impossible to find a class which has been renamed, merged or removed between Godot 3.X and Godot 4.0 without a diploma in Github archeology.

For example I am porting a Godot 3.X project to Godot4.0 which uses the File class. Godot 4.0 does not seem to have the File class. I want to rewrite my script with the appropriate 4.0 approach/replacement, but I am not able to find what the replacement solution is, despite online searching. Sifting through Github issues to figure out what happened is a very unpleasant user experience to put it mildly.

Ideally, I would be able to just switch from the stable (3.X) online documentation of the class I am interested in, to the latest online documentation and it would lead me automatically to the 4.0 replacement class.

Now I know the online docs are limited in functionality, so this might not be possible for whatever reason. But we could definitely have a margin box somewhere on the class page saying:

"This class will be removed/renamed in Godot4 to ClassName"

ClassName then links to the latest online docs page of the Godot4 class. Likewise the Godot4.0 replacement class could link back to the Godot 3.X class page with a similar text box, like:

"This class replaces the ClassName in Godot3.X " ... at least for a transition period.

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/stable/classes/class_file.html
https://docs.godotengine.org/en/latest/classes/class_fileaccess.html