pgsql: Re-order pg_attribute columns to eliminate some padding space.

Re-order pg_attribute columns to eliminate some padding space.

Now that attcompression is just a char, there's a lot of wasted
padding space after it.  Move it into the group of char-wide
columns to save a net of 4 bytes per pg_attribute entry.  While
we're at it, swap the order of attstorage and attalign to make for
a more logical grouping of these columns.

Also re-order actions in related code to match the new field ordering.

This patch also fixes one outright bug: equalTupleDescs() failed to
compare attcompression.  That could, for example, cause relcache
reload to fail to adopt a new value following a change.

Michael Paquier and Tom Lane, per a gripe from Andres Freund.

Discussion: https://postgr.es/m/20210517204803.iyk5wwvwgtjcmc5w@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f5024d8d7b04de2f5f4742ab433cc38160354861

Modified Files
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doc/src/sgml/catalogs.sgml           | 28 ++++++++++++++--------------
src/backend/access/common/tupdesc.c  | 16 +++++++++++-----
src/backend/access/spgist/spgutils.c |  4 ++--
src/backend/bootstrap/bootstrap.c    | 13 +++++++------
src/backend/catalog/genbki.pl        |  8 ++++----
src/backend/catalog/heap.c           | 19 ++++++++++---------
src/backend/catalog/index.c          | 10 ++++++----
src/backend/commands/tablecmds.c     | 28 ++++++++++++----------------
src/include/access/spgist_private.h  |  2 +-
src/include/catalog/catversion.h     |  2 +-
src/include/catalog/pg_attribute.h   | 22 +++++++++++-----------
11 files changed, 79 insertions(+), 73 deletions(-)