Auto merge of rust-lang#12847 - Veykril:vscode-downgrade, r=Veykril

fix: Fix restart server duplicating language clients

Reverts 03a62c1
vscode-languageclient@8.0.0-next.15 and beyond changed the behaviour of language clients to be automatically started if a request comes in while they are not running. Currently when we restart the server via the restart command we recreate the language client, which causes VSCode to restart the stopped server, effectively duplicating our language clients...

Reverting the commit is simpler right now, the proper fix would be to only create a language client once and then use the `restart` functionality on it instead.

Fixes rust-lang/rust-analyzer#12836