If delete all meta is set, make sure to delete associated post meta f…

[oscarssanchez]

…rom other posts

Description of the Change

Fixes #2461

There's a special case where if $delete_all is set (and it should be set if deleting an attachment for example) associated meta from other posts with the deleted post should be deleted as well.

Currently there's no action to know if this took place, but there's a filter which can be used to know the value of $delete_all to set a new property of the sync manager to later be used. As we will not be deleting post meta from a specific post, but all meta that's on a post and in the ES index, the PR retrieves the ES post that should not be updated yet, and simply reindexes it.

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Verification Process

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry