Use Pager instead of PagerSlim in ListPart admin view

[MikeAlhayek]

Currently, when editing item in a ListPart like blogposts, we get a PagerSlim in the admin. This is not a great experience since one may have many blogposts under the same blog.

This should be converted to a Pager instead allowing the same experience as when editing other content items.

[gvkries]

Related: #8367

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