pgsql: Add more tab completion support for ALTER DEFAULT PRIVILEGES in

Add more tab completion support for ALTER DEFAULT PRIVILEGES in psql.

This adds tab completion of "GRANT" and "REVOKE [GRANT OPTION FOR]"
for ALTER DEFAULT PRIVILEGES, and adds "WITH GRANT OPTION" for
ALTER DEFAULT PRIVILEGES ... GRANT ... TO role.

Author: Vignesh C, with cosmetic adjustments by me
Reviewed-by: Shubham Khanna, Masahiko Sawada
Discussion: https://postgr.es/m/CALDaNm1aEdJb-QJi%3DGWStkfj_%2BEDUK_VtDkn%2BTjQ2z7HyU0MBw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/304b6b1a6b7116bae30ea24119f04474eba7f0ed

Modified Files
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src/bin/psql/tab-complete.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)