If there are no pages when the customizer is opened, the `static_front_page` section will be hidden. As soon as a page is created in the customizer session, the `static_front_page` section will be revealed. Previously the section would not be registered if there were no pages. Page stubs created via nav menus will appear in the `dropdown-pages` controls for `page_for_posts` and `page_on_front`, and such page stubs will thus cause the `static_front_page` section to appear. Plugins that facilitate page creation in the customizer by filtering `get_pages` will also cause the section to appear.
See #34923.
Fixes#38013.
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