pgsql: Fix COPY FREEZE with CLOBBER_CACHE_ALWAYS

Fix COPY FREEZE with CLOBBER_CACHE_ALWAYS

This adds code omitted from commit 7db0cd2145 by accident, which had
two consequences. Firstly, only rows inserted by heap_multi_insert were
frozen as expected when running COPY FREEZE, while heap_insert left
rows unfrozen. That however includes rows in TOAST tables, so a lot of
data might have been left unfrozen. Secondly, page might have been left
partially empty after relcache invalidation.

This addresses both of those issues.

Discussion: https://postgr.es/m/CABOikdN-ptGv0mZntrK2Q8OtfUuAjqaYMGmkdU1dCKFtUxVLrg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/39b66a91bdebb00af71a2c6218412ecfc89a0e13

Modified Files
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src/backend/access/heap/heapam.c | 78 +++++++++++++++++++++++++++++++++++++++-
src/backend/access/heap/hio.c | 22 ++++++------
2 files changed, 88 insertions(+), 12 deletions(-)