Renamed classes should have redirects

[idbrii]

Your Godot version: 4.1.1

Issue description:

If I google for godot look_at, the top result is Spatial in Godot 3. When I switch to stable docs, I get "Page not found":
https://docs.godotengine.org/en/stable/classes/class_spatial.html

It would be great for the renamed classes to have a redirect to the new name to make it easier for people coming to godot from search results.

URL to the documentation page:

https://docs.godotengine.org/en/stable/classes/class_spatial.html

This page lists all the renames: https://docs.godotengine.org/en/latest/tutorials/migrating/upgrading_to_godot_4.html

[tetrapod00]

Related: #6897, #6615, #6260, #5591. But this isn't quite an exact duplicate of any of those.

Tagging this "3.x" because it's related to the migration experience