Command to list registered sidebars
Fix copy pasta
Update `WP_CLI\Utils\load_command()` to handle commands like `sidebar widget`

Previously, `load_command()` only supported commands where the name matched exactly (e.g. `wp post` and `post.php`). The `* meta` commands escaped this by defining their classes within the parent class file.

This change means `wp sidebar widget` will resolve to `sidebar-widget.php`, as well as `sidebar.php`
Introduce `wp sidebar widget` with list, update, and remove
Re-index the sidebar's list of widgets after a widget is removed
Move widgets between positions on a sidebar
Basic tests for sidebar widgets
Register the "Inactive Widgets" sidebar, because core doesn't normally do this for us
Sanitize a widget's options using its defined callback
Further abstraction that will be useful down the line
Utility functions for getting and updating options associated with a given widget
Support for adding a widget to a sidebar
Refactor to use new sidebar widget getter

Core's private function isn't doing it for us because it's dependent on the global
Update tests to include `wp sidebar widget update` case
Continue consolidation and refactor
Revert "Update `WP_CLI\Utils\load_command()` to handle commands like `sidebar widget`"

This reverts commit 16892f074fc2d688f267299cdfabd63c68e3bc27.

See https://github.com/wp-cli/wp-cli/commit/16892f074fc2d688f267299cdfabd63c68e3bc27#commitcomment-5951766
Rename and refactor to accommodate 77222f7967b989e174b75b2852d9fad66ae90bfa
Clarify why this method required re-implementing
Refactor: `widget-id` is a unique widget key we can use across the board
remove unnecessary casting to objects