Implement information_schema.parameters.parameter_default column

doc/src/sgml/information_schema.sgml

src/backend/catalog/information_schema.sql

src/backend/utils/adt/ruleutils.c

src/include/catalog/catversion.h

src/include/catalog/pg_proc.h

src/include/utils/builtins.h

src/test/regress/expected/create_function_3.out

src/test/regress/sql/create_function_3.sql