pgsql: REPACK CONCURRENTLY: fix processing of toasted tuples

REPACK CONCURRENTLY: fix processing of toasted tuples

In order to process tuples inserted or updated while REPACK executes, we
write those tuples to disk and later restore them; however, some forms
of toasted tuples were not being processed correctly. Fix that.

Also expand the tests a bit for better coverage.

Author: Satya Narlapuram <satyanarlapuram(at)gmail(dot)com>
Author: Antonin Houska <ah(at)cybertec(dot)at>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHg+QDeXb9HM2VGKXQedyCp52GzajJK5KOUdNi6oLjsS0nerQw@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6ca631b9901264b97c5b165e66edd3a85847ee0b

Modified Files
--------------
src/backend/commands/repack.c | 2 +-
.../injection_points/expected/repack_toast.out | 109 ++++++++++----
.../injection_points/specs/repack_toast.spec | 158 +++++++++++++++------
3 files changed, 199 insertions(+), 70 deletions(-)