cmd/cue: enable subcommand suggestions when a user makes a typo

We had disabled this a while back due to `cue foo` being allowed
as a shortcut to `cue cmd foo`. Since all the `cmd` subcommands
were not known upfront by cobra, any suggestions it made would be
missing information and potentially confuse users.

Since https://cuelang.org/issue/2519 was closed by removing support
for the deprecated `cue foo` short form, we can re-enable this now.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I9bfa385f5d1e68413d147123d0861ce27383f69a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1204874
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

cmd/cue/cmd/root.go

@@ -204,11 +204,6 @@ func New(args []string) (*Command, error) {
 		// We can explicitly trigger help on certain errors via pflag.ErrHelp.
 		SilenceErrors: true,
 		SilenceUsage:  true,
-
-		// We currently support top-level custom commands like `cue mycmd` as an alias
-		// for `cue cmd mycmd`, so any sub-command suggestions might be confusing.
-		// TODO(mvdan): remove this and test it, as we no longer support `cue mycmd`.
-		DisableSuggestions: true,
 	}
 
 	c := &Command{

cmd/cue/cmd/testdata/script/unknown_args.txtar

@@ -16,3 +16,7 @@ unknown command "unknown" for "cue"
 unknown flag: --unknown
 -- typo_cmd.stdout --
 unknown command "evla" for "cue"
+
+Did you mean this?
+	eval
+