pgsql: Separate out bytea sort support from varlena.c

Separate out bytea sort support from varlena.c

In the wake of commit b45242fd3, bytea_sortsupport() still called out
to varstr_sortsupport(). Treating bytea as a kind of text/varchar
required varstr_sortsupport() to allow for the possibility of
NUL bytes, but only for C collation. This was confusing. For
better separation of concerns, create an independent sortsupport
implementation in bytea.c.

The heuristics for bytea_abbrev_abort() remain the same as for
varstr_abbrev_abort(). It's possible that the bytea case warrants
different treatment, but that is left for future investigation.

In passing, adjust some strange looking comparisons in
varstr_abbrev_abort().

Author: Aleksander Alekseev <aleksander@tigerdata.com>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAJ7c6TP1bAbEhUJa6+rgceN6QJWMSsxhg1=mqfSN=Nb-n6DAKg@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/9303d62c6db0207b8c2649205f7bc9350c1f62db

Modified Files
--------------
src/backend/utils/adt/bytea.c    | 238 ++++++++++++++++++++++++++++++++++++++-
src/backend/utils/adt/varlena.c  |  43 ++-----
src/tools/pgindent/typedefs.list |   1 +
3 files changed, 242 insertions(+), 40 deletions(-)