MDEV-36523: Load basic stats from trace into optimizer

[bsrikanth-mariadb]

This task loads the stats of the tables that are used in a query,
from the trace into the optimizer. This feature is also controlled
by optimizer_record_context, and is not enabled by default.
The stats such as num_of_records present in the table, indexes if present,
their names, along with the average number of records_per_key
with in each index are loaded from the trace.
Additionally, stats from range analysis i.e. ranges, and the
corresponding number of records are also loaded from the trace.

The trace context which is in JSON format is firstly set into the
session variable optimizer_trace_stored_context.
Later, when a user issues a query, the contents of this variable is
parsed and an in memory representation is built using the class
Optimizer_context_replay. This class is then used by the optimizer
to update and save original values of the tables, indexes, and range stats
in the methods "set_statistics_for_table()" of sql_statistics.cc, and
"check_quick_select()" of opt_range.cc.
After the query gets finished, the statistics that were updated
in the optimizer are restored back to the saved original values.

The entry point for parsing the json structure is in
"mysql_execute_command()" of sql_parse.cc, and similarly exit point
i.e. to restore the saved stats of the optimizer is at the end
of the same method.

Two new warning/error messages are introduced:
ER_JSON_OPTIMIZER_REPLAY_CONTEXT_PARSE_FAILED, and
ER_JSON_OPTIMIZER_REPLAY_CONTEXT_MATCH_FAILED