Revert "Don't export UI schemas from top-level of package"

This reverts commit 0b5e199.

src/index.ts

@@ -2,6 +2,7 @@ export {
   rendererRegistryEntries,
   cellRegistryEntries,
 } from "./renderer-registry-entries"
+export type * from "./ui-schema"
 
 export { AlertLayout } from "./layouts/AlertLayout"
 export { BooleanControl } from "./controls/BooleanControl"