dev/core#3038 Fix handling for payment_instrument_id, cleanup financial_type_id

dev/core#3038 Fix handling for payment_instrument_id, cleanup financial_type_id

This addresses https://lab.civicrm.org/dev/core/-/issues/3038
by getting rid of the non-standardness around payment_instrument_id
and financial_type_id. The two fields are now
marked as importable and we use the
real names (payment_instrument_id) rather than the
'handy-dandy' names (payment_instrument) - which means
we can simplify in a bunch of places. Also since we are
already cleaning up names in the upgrade we add these in there