Block Hooks: Add apply_block_hooks_to_content_from_post_object

[ockham]

Port of WordPress/gutenberg#68926.

More details TBD.

Fixes #61074, #62716.

Trac ticket: https://core.trac.wordpress.org/ticket/62716

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[github-actions]

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[Mamaduka]

Adding a unit test for unhappy paths might be a good idea. When post_content returns something different due to the filter.

[Mamaduka]

@ockham, is this ready for review?

[ockham]

@ockham, is this ready for review?

Not quite yet -- I still need to increase test coverage, and audit other callsites of apply_block_hooks_to_content to see if they should be changed to call apply_block_hooks_to_content_from_post_object instead.

I won't be able to work on this PR this week, but I'll continue work next week. I hope that works for you time-wise, @Mamaduka?

[Mamaduka]

Thanks, @ockham!

That timeline should be okay for now. We just need to make sure this is merged before Beta 1.