perf: BaseDocument improvements (#15398)
perf: BaseDocument improvements (#15398)

* perf: BaseDocument improvements

* Add `default_fields_set`, use default placeholder to lookup fields in update(), refactor get_valid_columns()

* Revert all changes except "update()"

Co-authored-by: Gavin D'souza <6ffb0d8c50bc09d01d54428b8baf1689144565f4@gmail.com>
frappe/frappe,StrellaGroup/frappe,frappe/frappe,StrellaGroup/frappe,mhbu50/frappe,StrellaGroup/frappe,yashodhank/frappe,yashodhank/frappe,mhbu50/frappe,mhbu50/frappe,almeidapaulopt/frappe,mhbu50/frappe,frappe/frappe,almeidapaulopt/frappe,yashodhank/frappe,yashodhank/frappe,almeidapaulopt/frappe,almeidapaulopt/frappe