Refactoring Table.ChangeType to share value transformation logic

[bgribaudo]

Existing uses one set of logic to handle table column value transforms and another for record field value/list item transforms. This change DRYs the code to remove this duplication.

/CC: @CurtHagenlocher

[bgribaudo]

@CurtHagenlocher, @ptyx507x, thought I would check in on this. :-) Do you know if this has any chance of moving forward, or should it be closed?

Thanks!