pgsql: amcheck: Normalize index tuples containing uncompressed varlena

amcheck: Normalize index tuples containing uncompressed varlena

It might happen that the varlena value wasn't compressed by index_form_tuple()
due to current storage parameters.  If compression is currently enabled, we
need to compress such values to match index tuple coming from the heap.

Backpatch to all supported versions.

Discussion: https://postgr.es/m/flat/7bdbe559-d61a-4ae4-a6e1-48abdf3024cc%40postgrespro.ru
Author: Andrey Borodin
Reviewed-by: Alexander Lakhin, Michael Zhilin, Jian He, Alexander Korotkov
Backpatch-through: 12

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b1fe8efdf17eb4877f7c4c31c85111ec740ad872

Modified Files
--------------
contrib/amcheck/expected/check_btree.out | 10 ++++++++++
contrib/amcheck/sql/check_btree.sql      |  6 ++++++
contrib/amcheck/verify_nbtree.c          | 13 +++++++++++++
3 files changed, 29 insertions(+)