Description

In this NULL skew optimizer, we will add a new project node under the join node, which currently does not carry the stats equivalent node from HBO, hence lose the HBO information.
Previously I think it's fine, as the the project node adds a few more columns, i.e. new join keys which is of string type. However, in recent debug, I found that this will lead to use of inaccurate CBO stats. HBO stats may have the reported size larger than it should be, which is because of the new join keys added, however the row count is still accurate and the size is still not far away since the new join key is usually small.
In this PR I keep the stats equivalent node in HBO.

Motivation and Context

As in description

Impact

More accurate stats

Test Plan

Existing unit tests

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== RELEASE NOTES ==

General Changes
* Fix randomize null join optimizer to keep HBO information for join input