fix(split-button): ensure prop type definition is exported from index…

….d.ts file

Exports the prop type definition from the index file as well as the functional component

fix #5049

src/components/split-button/index.d.ts

@@ -1 +1,2 @@
 export { default } from "./split-button";
+export type { SplitButtonProps } from "./split-button";