get correct row counts into SHOW TABLE STATUS

[mdcallag]

We can get an estimate for the row count via ('Rows:' below is always 10,000 today) via RocksDB property "rocksdb.estimate-num-keys".

Data_length and index_length are best defined when not using an index-organized table. For an index-organized table like InnoDB, the data_length column includes the size of the PK index (including all columns) and the index_length column has the size of all secondary indexes. We can treat RocksDB in the same way. However, we aren't using file-per-table or file-per-index for RocksDB so we need to determine whether we can get estimates on index sizes.

mysql -e 'show table status\G' iok1

*************************** 1. row ***************************
Name: ai
Engine: ROCKSDB
Version: 10
Row_format: Dynamic
Rows: 1000
Avg_row_length: 0
Data_length: 0
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: NULL
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
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