`renderDisclosureContent` in `preset_fields.js` tries to detect the geometry types of the selected entities, but the result is always `[]`.
Reason: The handler of `_entityIDs.reduce` always returns `true`. So the result of the `reduce` call is `true` as well. `Object.keys(true)` results in `[]`.
Fix: The handler of `_entityIDs.reduce` should return the map which collects the geometry types, so `geometries` will be be something like `["line", "vertex"]`.
Consolidate localization behavior and init to a coreLocalizer function and singleton
Explicitly support `en-US` locale
Rename coreData to coreFileFetcher and export a singleton rather than using a property of coreContext
Add `apiConnections` property of coreContext to simplify adding a source switcher
Replace some init functions with re-callable, promise-supporting `ensureLoaded` functions
Make coreContext itself load the UI if a container has been specified at init time
Fix code tests
