Adds the `'sidebar_admin-setup'`, `'sidebar_admin_page'`, and
`current_theme_supports( 'widgets' )` check to the widgets block editor so that
the block editor screen is more compatible with the classic screen.
Fixes#53288.
Props isabel_brison.
git-svn-id: https://develop.svn.wordpress.org/trunk@51061 602fd350-edb4-49c9-b593-d223f7449a82
Moves the widgets block editor from Gutenberg into WordPress Core.
- Adds @wordpress/edit-widgets, @wordpress/customize-widgets and
@wordpress/widgets.
- Modifies wp-admin/widgets.php to branch between the old editor and new editor
depending on wp_use_widgets_block_editor().
- Modifies WP_Customize_Widgets to branch between the old editor control and new
editor control depending on wp_use_widgets_block_editor().
Follows [50996] which was missing these files.
See #51506.
Props isabel_brison, TimothyBlynJacobs, andraganescu, kevin940726, talldanwp.
git-svn-id: https://develop.svn.wordpress.org/trunk@50997 602fd350-edb4-49c9-b593-d223f7449a82
