Support rewriting subquery expressions in simplify_expressions

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
PR #3764 reverts a regression in optimizing subqueries but does so by running simplify_expressions a second time, after subqueries have been converted to joins.

This is not the ideal solution.

Describe the solution you'd like
simplify_expressions should rewrite subqueries instead. This will support all subqueries, not just the ones that can be converted to joins.

Describe alternatives you've considered
None

Additional context
See conversation #3764 (comment)

[HaoYang670]

Do we need to consider the schema infomation of the parent query when optimizing the subquery?