Retain the ordering of fields in the table schema when creating the projection for an update plan

[avantgardnerio]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Presently, when planning an update statement, the order of the fields gets alphabetized due to the use of a BTreeMap. It would be tidier (and solve a bug in our own project) if the order was guaranteed to be the same as the order in the shema of the table.

Describe the solution you'd like

Remove the BTreeMap

Describe alternatives you've considered

Force consumers to be tolerant of order differences.