This is an automated cherry-pick of #39467

What problem does this PR solve?

Issue Number: close #39466

Problem Summary:

To implement a ttl job scheduler, we'll need a local map for info schema and ttl table status, to map from a physical table id to related schema information and the information stored in the ttl table status

What is changed and how it works?

It does the following changes:

1. Refine the code structure. The sql generator and cache are split and placed in different directories. If we are using sql generator and cache from the manager, both placing them in one level and "reverse (about the folder hierarchy) dependency" is not suggested.
2. Move codes related with session into ttl/session, and add an interface of session pool into it (though there are some existing session pool, with the same definition here). I don't know whether it appropriate to add yet another session pool interface (but others are in extensions, br... pkg).
3. Add two struct: InfoSchemaCache and the TTLTableStatusCache. They are the local mirror of the info schema and mysql.tidb_ttl_table_status system table.

This PR relies on #39315. Please merge it before this one.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code