pgsql: Refactor ParamListInfo initialization

Refactor ParamListInfo initialization

There were six copies of identical nontrivial code.  Put it into a
function.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c6ff0b892c30122b75d32c524109d16ee3c973f0

Modified Files
--------------
src/backend/commands/prepare.c   | 12 +-------
src/backend/executor/functions.c | 15 ++--------
src/backend/executor/spi.c       | 17 ++----------
src/backend/nodes/params.c       | 59 +++++++++++++++++++++-------------------
src/backend/tcop/postgres.c      | 11 +-------
src/include/nodes/params.h       |  1 +
src/pl/plpgsql/src/pl_exec.c     |  3 +-
7 files changed, 40 insertions(+), 78 deletions(-)