internal/slices: move from internal/mod/mvs/internal/slices

We want to be able to use it from other places and we can't
use it from the Go standard library yet.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: I5e9f46b2843af19703273e24e6ada525556b8788
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1172863
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: rogpeppe

internal/mod/mvs/graph.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"sort"
 
-	"cuelang.org/go/internal/mod/mvs/internal/slices"
+	"cuelang.org/go/internal/slices"
 )
 
 // Versions is an interface that should be provided by implementations