Update hierarchy when deleting hierarchical CPT

[duck_]

When deleting a CPT post which is hierarchical its children don't have their post_parent properties updated. This updating code should be split out of the page specific branches into an is_post_type_hierarchical() check.

Noticed when patching #19636.

[duck_]

Patch switches to clean_post_cache() from clean_page_cache() for is_post_type_hierarchical() children. This is because the page clean function does some page specific stuff that doesn't need to occur for each child or for non-page content types, and clean_post_cache() does the recursive cleaning normally anyway.

[duck_]

In [19734]:

Update hierarchy for all hierarchical post types when deleting a parent post, not just for pages. Fixes #19637.