Harmonize parameter names in ecpg code.

Harmonize parameter names in ecpg code.

Make ecpg function declarations consistently use named parameters.  Also
make sure that the declarations use names that match corresponding names
from function definitions.

Like other recent commits that cleaned up function parameter names, this
commit was written with help from clang-tidy.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAH2-WznJt9CMM9KJTMjJh_zbL5hD9oX44qdJ4aqZtjFi-zA3Tg@mail.gmail.com