Add, fix, update bookmark related functions

[IanDelMar]

• Return type narrowing for
  • add_link(),
  • edit_link(),
  • get_bookmark_field(),
  • get_default_link_to_edit(),
  • sanitize_bookmark_field(),
  • wp_get_link_cats()
• Parameter type narrowing for
  • get_bookmark_field()
  • sanitize_bookmark_field()
• get_default_link_to_edit() marked impure (return value depends on $_GET)
• Fix for wp_update_link()
• Reorganised tests for these functions

Notes

• add_link(), edit_link(), and wp_update_link() all call wp_insert_link() with the default $wp_error value (false). Therefore, none of these functions returns WP_Error. (For wp_update_link() the documentation was misleading; and I incorrectly added WP_Error to the return type in Narrow return type of wp_update_link() #357.)
• The $field parameter has been narrowed for get_bookmark_field() and sanitize_bookmark_field() to be a key of the $linkdata array (see wp_insert_link()). Enforcing this allows the return type to be narrowed accurately. For get_bookmark_field(), the documented type was incorrect; compared with the documented type, the actual return type is wider.
• Tests reorganised: all admin-related bookmark functions are now in bookmark-admin.php; general bookmark functions are in bookmark.php.

Hopefully, this is the end of my bookmarks journey. 🙂

[szepeviktor]

As far as I remember bookmarks are disabled in WordPress ...

[IanDelMar]

Well, 😂