[PATCH] psql: Complete INDEX after REPACK USING

Hi hackers,

After manually typing `REPACK USING ` and pressing Tab, psql inserts
another `USING INDEX`, producing `REPACK USING USING INDEX`. After an
explicit table name, `REPACK tab1 USING ` offers no completion.

The attached fix completes `INDEX` after `USING`, with or without an
option list, table name, or column list.

Regression tests are attached as a separate patch.

I tested on master with assertions enabled. The new tests fail without
the fix, and all psql TAP tests pass with it.

I have also posted a separate fix for index completion after a
`REPACK` column list [1]. The two fixes are independent.

[1]
https://www.postgresql.org/message-id/CAG7L5%2B7Xmus%2BJLa0m%3DLpw49wU%3DsecPm5dzNd2ibmfvhdSYEfqA%40mail.gmail.com

Thanks,
Sho

--
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*Sho Ito (Sean)*

E-mail: i(dot)sho(dot)0628(at)gmail(dot)com
LinkedIn: *https://www.linkedin.com/in/sho-ito-0628/
<https://www.linkedin.com/in/sho-ito-0628/>*
GitHub: https://github.com/sean0628/
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