[Block Library]: Update the relationship of some posts needed inside Query Loop to ancestor

[ntsekouras]

What?

This PR just add a bit more flexibility to the insertion of Post Template, No results and Pagination inside a Query Loop block. Previously you could insert them through the inserter only if they were direct parents of Query Loop, but now they can be inserted in nested blocks(ex Group), as long as they have Query Loop as an ancestor.

Testing Instructions

1. Inside a Query Loop block add a Group and then insert through the inserter Post Template, No results or Pagination blocks.
2. The above three blocks cannot be inserted through the inserter if they don't have a Query Loop ancestor.
3. No regressions are introduced and everything else should work as before.

[gziolo]

Was there any discussion about which blocks could benefit from using ancestor instead of parent? Comments block could also get similar updates wherever applicable:

Actually, it's the only block that uses that API, but in a slightly different way than this PR explores.

It also made me wonder whether the Comments block doesn't use ancestor for the Comment Template block to avoid the risk of inserting the block into self.

[ntsekouras]

Was there any discussion about which blocks could benefit from using ancestor instead of parent?

In various issues at some point, but not a separate issue. We also introduced a new Query Loop PR that wraps these blocks inside Group blocks. That was my main trigger for this PR right now. I think the main reason for some comment blocks to use this API, is because they cannot work outside of this context at all.

It also made me wonder whether the Comments block doesn't use ancestor for the Comment Template block to avoid the risk of inserting the block into self.

That's a good point and is something we might not want for Post Template... Maybe @ockham or @c4rl0sbr4v0 could share some insights?

[webmandesign]

+1 This would really be great! It would most likely solve my issue #48296 when I want to use core/query-pagination (and also core/comments-pagination) as a Template Part or Pattern.