pgsql: psql: Improve tab-completion for MERGE.

psql: Improve tab-completion for MERGE.

Commit 7103ebb7aa added the tab-completion for MERGE accidentally
in the middle of that for LOCK TABLE. This commit fixes this issue.

This also adds some tab-completion for MERGE.

Back-patch to v15 where MERGE was introduced.

Author: Kotaro Kawamoto, Fujii Masao
Reviewed-by: Shinya Kato, Álvaro Herrera
Discussion: https://postgr.es/m/9f1ad2a87a58cd5e7d64f3993130958d@oss.nttdata.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9a6915257d1d804ddba05331030b74d7426a4005

Modified Files
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src/bin/psql/tab-complete.c | 102 +++++++++++++++++++++++++++++---------------
1 file changed, 67 insertions(+), 35 deletions(-)