[IMP] misc: export the validate function

The props validation code is actually quite difficult to get right.
Also, it is sometimes useful to be able to validate an object against a
specified schema. Therefore, this commit exports the standalone validate
function as an utility function.

src/index.ts

@@ -52,5 +52,6 @@ export {
   onWillDestroy,
   onError,
 } from "./component/lifecycle_hooks";
+export { validate } from "./validation";
 
 export const __info__ = {};