This is prep work for #1443, pulled out of #1467.

Prior to this PR, we bundled Geoblacklight's JS separately from the generated app's JS. This was done because we have to manage the registration of all of the stimulus controllers and then call all the initializer functions that make up the GBL core before the app's JS runs, so they are available.

After this PR, Geoblacklight's JS is more extendable & interoperable due to borrowing a paradigm from Blacklight. You can now do:

import "@geoblacklight/frontend"

which is all that's needed to register the controllers and ensure everything is set up. You can also do:

import Geoblacklight from "@geoblacklight/frontend"
Geoblacklight.onLoad(() => console.log('my thing'))

to run arbitrary code after Geoblacklight is set up, just like Blacklight's onLoad hook. This hook also fires whether or not you're using Turbo. Individual controllers and modules can still be imported, e.g. if you wanted to subclass them:

import { LeafletViewerController } from "@geoblacklight/frontend"
class MyNewViewerController extends LeafletViewerController {
  // ...
}

Because of this, the application now only needs a single unified JS entrypoint, where we import Geoblacklight and then add any other JS we want. The whole thing is bundled into a single file by Vite.