Add command deprecation

[Tyriar]

Instead of just changing command names, we should slowly phase them out and presenting warnings if the old ones are being relied upon and direct users to the new commands. Adjusting to #6605 (comment) may be easier that way, not totally destroying any custom keybindings and informing the user in a visible way of the change without the need to read the release notes.

This would also allow any clean up of command names to be done with a smaller impact to the end user.

[bpasero]

Actually maybe we could register all the old command ids and just show a message to the user telling him the new identifier of this command!

[Tyriar]

Great! Something like that is what I had in mind 👍

[bpasero]

@Tyriar assigning to you for verification.

[Tyriar]

Thanks for putting this together!