pgsql: Include error location in errors from ComputeIndexAttrs().

Include error location in errors from ComputeIndexAttrs().

Make use of IndexElem's new location field to localize these
errors better.

Author: jian he <jian.universality@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxH3OgXF1hrzGAaWyNtye2jHEmk9JbtrtGv-KJK6tsGo5w@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/ba75f717526cbaa9000b546aac456e43d03aaf53

Modified Files
--------------
src/backend/bootstrap/bootparse.y                  |  6 ++-
src/backend/commands/indexcmds.c                   | 61 +++++++++++++++-------
src/backend/commands/tablecmds.c                   |  9 ++--
src/backend/tcop/utility.c                         |  3 +-
src/include/commands/defrem.h                      |  3 +-
src/test/regress/expected/alter_table.out          |  4 ++
src/test/regress/expected/collate.icu.utf8.out     |  2 +
src/test/regress/expected/collate.linux.utf8.out   |  2 +
src/test/regress/expected/collate.out              |  2 +
.../regress/expected/collate.windows.win1252.out   |  2 +
src/test/regress/expected/sqljson_queryfuncs.out   | 56 ++++++++++++++++++++
11 files changed, 123 insertions(+), 27 deletions(-)