Non-breakable refactoring according `postgres_fdw` before initial `RETURNING` implementation #626

Job	Run time
detect-pgversion	4s
Test on PostgreSQL 13.15, postgis mode	7m 2s
Test on PostgreSQL 14.12, postgis mode	8m 2s
Test on PostgreSQL 16.3, postgis mode	7m 19s
Test on PostgreSQL 13.15, default mode	4m 17s
Test on PostgreSQL 15.7, postgis mode	7m 3s
Test on PostgreSQL 17.0, default mode	5m 30s
Test on PostgreSQL 16.3, default mode	4m 50s
Test on PostgreSQL 15.7, default mode	5m 14s
Test on PostgreSQL 14.12, default mode	4m 56s
Test on PostgreSQL 17.0, postgis mode	8m 20s
	1h 2m 37s

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