pgsql: postgres_fdw: Remove duplicate code in DML execution callbackfu

postgres_fdw: Remove duplicate code in DML execution callback functions.

postgresExecForeignInsert(), postgresExecForeignUpdate(), and
postgresExecForeignDelete() are coded almost identically, except that
postgresExecForeignInsert() does not need CTID.  Extract that code into
a separate function and use it in all the three function implementations.

Author: Ashutosh Bapat
Reviewed-By: Michael Paquier
Discussion: https://postgr.es/m/CAFjFpRcz8yoY7cBTYofcrCLwjaDeCcGKyTUivUbRiA57y3v-bw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6c61d7c5935793e218d2335ac540a2cea7eacdce

Modified Files
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contrib/postgres_fdw/postgres_fdw.c | 283 +++++++++++++-----------------------
1 file changed, 103 insertions(+), 180 deletions(-)