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