Call hook_civicrm_post with op 'merge' after contacts are merged

When two contacts are merged, all related data is moved via SQL statements. This means that post-edit hooks are not called for any changes in the related information, such as contributions.

As a developer using an extension to recalculate view-only custom fields when contributions change, I want to be able to recalculate the fields after the merge is complete.

Hook civicrm_merge is not what I need, as that allows extensions to modify table lists and sql statements, but not to perform custom calculations. Currently after merging contacts, hook civicrm_post is called with 'trash' and then with 'delete' against the old contact, but no hook is called with the new contact after the merge is complete.

I propose calling hook_civicrm_post with op='merge' and a reference to the target contact after the merge is complete, allowing extensions to recalculate view-only custom fields with the merged data.