Summary of changes

- MD_CTX_SIZE is increased

- EVP_CIPHER_CTX_buf_noconst(ctx) does not work anymore, points
  to nobody knows where. The assumption made previously was that
  (since the function does not seem to be documented)
  was that it points to the last partial source block.
  Add own partial block buffer for NOPAD encryption instead

- SECLEVEL in CipherString in openssl.cnf
  had been downgraded to 0, from 1, to make TLSv1.0 and TLSv1.1 possible
   (according to https://github.com/openssl/openssl/blob/openssl-3.0.0/NEWS.md
   even though the manual for SSL_CTX_get_security_level claims that it
   should not be necessary)

- Workaround Ssl_cipher_list issue, it now returns TLSv1.3 ciphers,
  in addition to what was set in --ssl-cipher

- ctx_buf buffer now must be aligned to 16 bytes with openssl(
  previously with WolfSSL only), ot crashes will happen

- updated aes-t , to be better debuggable
  using function, rather than a huge multiline macro
  added test that does "nopad" encryption piece-wise, to test
  replacement of EVP_CIPHER_CTX_buf_noconst

GCC does not understand that the variable have_ndv determines
whether the variable ndv_ll is initialized. Let us add a
redundant initialization to pacify GCC.

The test innodb.log_file_size would occasionally fail with
an assertion failure !buf_pool.any_io_pending(). Let us wait
for the page cleaner thread to become idle already in
srv_prepare_to_delete_redo_log_file(), like we used to.

MTR still uses JSON_HB as the default.

In Histogram_json_hb::point_selectivity(), do return selectivity of 0.0
when the histogram says so.

The logic of "Do not return 0.0 estimate as it causes a multiply-by-zero
meltdown in cost and cardinality calculations" is moved into
records_in_column_ranges() where it is one *once* per column pair (as
opposed to doing once per range, which can cause the error to add-up
to large number when there are many ranges)

Followup: remove this line from get_column_range_cardinality()

      set_if_bigger(res, col_stats->get_avg_frequency());

and make sure it is only used with the binary histograms.
For JSON histograms, it makes the estimates unnecessarily imprecise.

Added a testcase

Fix special handling for values that are right next to buckets with ndv=1.

Fix the code in Histogram_json_hb::range_selectivity that handles
special cases: a non-inclusive endpoint hitting a bucket boundary...

In read_bucket_endpoint(), handle all possible parser states.

Encode such characters in hex.

Save extra information in the histogram:

    "target_histogram_size": nnn,
    "collected_at": "(date and time)",
    "collected_by": "(server version)",

Also report JSON histogram load errors into error log, like it is already
done with other histogram/statistics load errors.

Add test coverage to see what happens if one upgrades but does NOT run
mysql_upgrade.

Previous JSON parser was using an API which made the parsing
inefficient: the same JSON contents was parsed again and again.

Switch to using a lower-level parsing API which allows to do
parsing in an efficient way.

- Make Histogram_json_hb::range_selectivity handle singleton buckets
  specially when computing selectivity of the max. endpoint bound.
  (for min. endpoint, we already do that).

- Also, fixed comments for Histogram_json_hb::find_bucket

When loading the histogram, use table->field[N], not table->s->field[N].

When we used the latter we would corrupt the fields's default value. One
of the consequences of that would be that AUTO_INCREMENT fields would
stop working correctly.

Handle the case where the last value in the table cannot be represented
in utf8mb4.

.. for non-existent values.

Handle this special case.

Fix a bug in position_in_interval(). Do not overwrite one interval endpoint
with another.

The problem was introduced in fix for MDEV-26724. That patch has made it
possible for histogram collection to fail. In particular, it fails for
non-assigned characters.

When histogram construction fails, we also abort the computation of
COUNT(DISTINCT). When we try to use the value, we get valgrind failures.

Switched the code to abort the statistics collection in this case.

When computing bucket_capacity= records/histogram->get_width(), round
the value UP, not down.

Part#3:
- make json_escape() return different errors on conversion error
  and on out-of-space condition.
- Make histogram code handle conversion errors.

Fix the description

Change it to LONGBLOB.
Also, update_statistics_for_table() should not "swallow" an error
from open_stat_tables.

.. part#2: correctly pass the charset to JSON [un]escape functions

MDEV-26595: ASAN use-after-poison my_strnxfrm_simple_internal / Histogram_json_hb::range_selectivity

Add testcase

Item_func_decode_histogram::val_str should correctly set null_value
when "decoding" JSON histogram.

Correctly handle empty string when [un]escaping JSON