infoschema v2 can not handle massy count of partition tables

[tiancaiamao]

Enhancement

This is a known issue when we develop infoschema v2

Ref #50959

Infoschema v2 aims to handle 1M tables, by keeping only "db name + table name => table id" in memory,
while make "table id => table info" cacheable.

But it does not handle partition table, all partition table info are still in memory.

Recently we found if the user have a lot partition tables, and continuously truncate partition, v2 seems to be regression.