Restructure core plugins, named exports to default export (#5592)

* use export default instead of named exports

I'm a little sad about this change, but it turns out that the order is
not guaranteed for named exports in ESM. It was the correct order in our
tests because of babel, but not in native ESM.

* update imports

Author: RobinMalfait

scripts/create-plugin-list.js

@@ -1,4 +1,4 @@
-import * as corePlugins from '../src/corePlugins'
+import corePlugins from '../src/corePlugins'
 import fs from 'fs'
 import path from 'path'