Add support for native JavaScript Modules

Unfortunately dynamic imports and .mjs extensions aren’t supported by the js helper.
Plugins also don’t create symlinks in the media folder.
It would be great to have native js modules supported.

@Ahmet Bora does https://github.com/getkirby/kirby/pull/3444 solve this suggestion?

I don’t fully understand with meaing js() helper but If what is meant is the ability to load .mjs files within the plugin, yes.