* based on RANGE pruning by COLUMNS (sys_trx_end) condition
* removed DEFAULT; AS OF NOW is always last; current VERSIONING as last non-empty (or first empty)
* Min/Max stats in TABLE_SHARE
* ALTER TABLE ADD PARTITION adds before AS OF NOW partition
* one `AS OF NOW`, multiple `VERSIONING` partitions;
* rotation of `VERSIONING` partitions by record count, time period;
* rotation is multi-threaded;
* conventional subpartitions as bottom level for versioned partitions;
* `DEFAULT` keyword selects first `VERSIONING` partition;
* ALTER TABLE ADD/DROP partition;
* REBUILD PARTITION basic operation.
