Uncorrelated query performance checker

[Philip Stoev]

It is possible to test the performance of uncorrelated subqueries by extracting them from the outer query and running them separately.

If the extracted query takes less time to execute v.s. executing the initial query with the subquery values inlined, then the optimizer plan that was chosen was inferior to manually decomposing the query using a higher-level language.

This can be implemented in the InlineSubqueries Validator by introducing a separate TRANSFORM_PERFORMANCE_INFERIOR tag that will mark the Transform as failed if the transformed, inlined query took substantially longer than the original query.