[Draft] Post Locking

[allan23]

Context

This is a draft PR of the Post Locking implementation (#3126)

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[swissspidy]

This could just use wp_set_post_lock(). No need to duplicate this code from core.

[allan23]

Is that function available via the REST API?

[swissspidy]

Ah, good point.

wp-admin/includes/post.php would need to be loaded in the REST API.

But we cannot just copy the core code for license reasons.

[swissspidy]

This could just use wp_check_post_lock(). No need to duplicate this code from core.

[swissspidy]

@allan23 Would be great if you could sign the CLA above so we could build upon your contribution here.

[allan23]

@googlebot I signed it!

[spacedmonkey]

Closing in favor of #6497