[REF] SavedSearch - additional cleanup & bugfixes

[colemanw]

Overview

Followup on #17003 - does some cleanup and refactoring to improve SaveSearch code.

Before

Alter queries using string manipulation.

After

Use class methods to alter queries.

[civibot]

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[eileenmcnaughton]

I went though the code & all the changes make sense.

I also tested creating a custom search smart group & a search builder smart group and in each case I was successfully able to take an action on the group's participants

[colemanw]

@eileenmcnaughton thanks for the review :)