* Eliminate need to pass both ID and instance in calls to `Values#add()` for panels, sections, controls, settings, partials, and notifications.
* Eliminate need to supply `content` param when constructing a `Control`.
* Unwrap the `options.params` object passed in constructors to just pass a flat `options`. (Back-compat is maintained.)
* Add support for `templateId` param for `Control` to override which template is used for the content.
* Remove unused `previewer` being supplied in `Control` instances.
* Rename `classes` to `containerClasses` on `Notification`.
* Automatically supply `instanceNumber` to improve stable sorting.
* Use `api.Notifications` for notifications in settings instead of `api.Value`.
See #30741.
Fixes#42083.
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