react-select: Allow placeholder to be an Element (#9061)

react-select/react-select.d.ts

@@ -173,7 +173,7 @@ declare namespace ReactSelect {
          * field placeholder, displayed when there's no value
          * @default "Select..."
          */
-        placeholder?: string;
+        placeholder?: string | __React.ReactElement<any>;
         /**
          * whether to enable searching feature or not
          * @default true;