✨(react) add Loader component

The first use of this loader will be inside the DataGrid for its
loading state. Its colors are based on the existing primary
colors tokens.

packages/react/src/index.ts

@@ -1,5 +1,6 @@
 import "./index.scss";
 
 export * from "./components/Button";
+export * from "./components/Loader";
 export * from "./components/Pagination";
 export * from "./components/Provider";