Register default post types before plugins and themes are loaded

[ryan]

Although correct behavior is to wait until init has fired to do anything, many themes call get_pages() prior to init. If the default post types have not been registered yet, get_pages() will fail because the "page" post type is not present. We can work around this in the same manner as we did for taxonomies by calling create_initial_post_types() before loading plugins and themes.

Works for me. Closing #12873 as a duplicate.

Wow, my search for existing tickets on the issue was obviously a failure. :-)

(In [14041]) Call create_initial_post_types() before plugins and themes are loaded so that premature post API calls don't fail. fixes #12918