Refactor ExpressionOptimizer

[tdcmeehan]

Description

Refactor ExpressionOptimizer to consistently return RowExpression. Before, ExpressionOptimizer would return RowExpression only for the method which did not take in a variable resolver function. I cannot discern a good reason for this. By refactoring this interface and making them both return RowExpression, and documenting that the two methods are equivalent when an identity function is used for the variable resolver, it becomes possible to share code that uses both methods.

Motivation and Context

This is to help address PR review feedback here: #24144 (comment)

Impact

Code refactoring. Implementations of ExpressionOptimizer in the SPI will need to update their plugins to accommodate the changed API.

Test Plan

Unit tests

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• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
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Release Notes

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== RELEASE NOTES ==

SPI Changes
* Improve ExpressionOptimizer#optimize method with a variable resolver to return ``RowExpression``. :pr:`24287`

[ZacBlanco]

Don't forget to update the release note with the correct PR #

[hantangwangd]

Thanks for this refactor, LGTM!

[rschlussel]

is it possible to change RowExpressionInterpreter to return a RowExpression instead of an object (seems like basically it requires wrapping any "values" in constant expressions, and then changing anything that calls it to expect that to happen). Returning an Object that could be anything and leaving it to the caller be able to handle it seems like a bad pattern to begin with.

[rschlussel]

but this change is still an improvement, so i'm fine with merging this first.