cmd/gazelle: add resolvers for activated languages only

This disables processing of rules for languages which are disabled via the -lang
flag. Concretely, this halves the time it takes for Gazelle to update our Go
rules by skipping processing of all closure_js rules.

cmd/gazelle/fix-update.go

@@ -245,6 +245,14 @@ func runFixUpdate(cmd command, args []string) (err error) {
 	loads := genericLoads
 	for _, lang := range languages {
 		cexts = append(cexts, lang)
+	}
+
+	c, err := newFixUpdateConfiguration(cmd, args, cexts)
+	if err != nil {
+		return err
+	}
+
+	for _, lang := range filterLanguages(c, languages) {
 		for kind, info := range lang.Kinds() {
 			mrslv.AddBuiltin(kind, lang)
 			kinds[kind] = info
@@ -253,11 +261,6 @@ func runFixUpdate(cmd command, args []string) (err error) {
 	}
 	ruleIndex := resolve.NewRuleIndex(mrslv.Resolver)
 
-	c, err := newFixUpdateConfiguration(cmd, args, cexts)
-	if err != nil {
-		return err
-	}
-
 	if err := fixRepoFiles(c, loads); err != nil {
 		return err
 	}