Comments: Add a `@since` note to the `wp_update_comment_data` filter about...

Comments: Add a `@since` note to the `wp_update_comment_data` filter about returning a `WP_Error` value.

Remove the ability to short-circuit comment update by returning `false` from the filter for now.

This was inconsistent with the `pre_comment_approved` filter, and should not be necessary if a more descriptive reason can be given by always using `WP_Error`.

See #39732.
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git-svn-id: https://core.svn.wordpress.org/trunk@47999 1a063a9b-81f0-0310-95a4-ce76da25c4cd