pgsql: Add parse location to IndexElem.

Add parse location to IndexElem.

This patch mostly just fills in the field, although a few error
reports in resolve_unique_index_expr() are adjusted to use it.
The next commit will add more uses.

catversion bump out of an abundance of caution: I'm not sure
IndexElem can appear in stored rules, but I'm not sure it can't
either.

Author: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Co-authored-by: jian he <jian(dot)universality(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CACJufxH3OgXF1hrzGAaWyNtye2jHEmk9JbtrtGv-KJK6tsGo5w@mail.gmail.com
Discussion: https://postgr.es/m/202512121327.f2zimsr6guso@alvherre.pgsql

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/62299bbd90d69e2273d3e2ba35af5953d20ca037

Modified Files
--------------
src/backend/bootstrap/bootparse.y | 1 +
src/backend/nodes/nodeFuncs.c | 3 +++
src/backend/parser/gram.y | 5 +++++
src/backend/parser/parse_clause.c | 11 ++++-------
src/backend/parser/parse_utilcmd.c | 6 ++++++
src/include/catalog/catversion.h | 2 +-
src/include/nodes/parsenodes.h | 1 +
src/test/regress/expected/insert_conflict.out | 6 +++---
8 files changed, 24 insertions(+), 11 deletions(-)