Fix i18next dir() return type to be "ltr" | "rtl" (#27069)

types/i18next/index.d.ts

@@ -493,7 +493,7 @@ declare namespace i18next {
         /**
          * Returns rtl or ltr depending on languages read direction.
          */
-        dir(lng?: string): void;
+        dir(lng?: string): "ltr" | "rtl";
 
         /**
          * Exposes interpolation.format function added on init.

types/i18next/v2/index.d.ts

@@ -128,7 +128,7 @@ declare namespace i18n {
 
         loadLanguages(lngs: string[], callback?: () => void): void;
 
-        dir(lng?: string): string;
+        dir(lng?: string): "ltr" | "rtl";
 
         createInstance(options?: Options, callback?: (err: any, t: TranslationFunction) => void): I18n;