This change enables the new defers analyzer in gopls.
It also adds it to the vet compatibility test.
A follow-up change will add it to vet itself.

Also, remove stray backquote in doc comment.

Updates golang/go#60048

Change-Id: I42f09bb79fcbe4e48593dd32fd066ddd39b9626f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/502975
Run-TryBot: Alan Donovan <adonovan@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>