Transfer tidb_xxxx components to pingcap org

[BusyJay]

Due to historical reasons, components like tidb_query_aggr, tidb_query_expr etc. are put in tikv repository as they are part of coprocessor. But it may not be a good choice as they are highly tidb specific, may not suitable for a general KV project. And we also lack of active maintainers/committers for these components. So I suggest to move these components to pingcap org.

The components to be moved include:

• tidb_query_expr
• tidb_query_codegen
• tidb_query_common
• tidb_query_datatype
• tidb_query_executors

They also depend on some of internal components including

• log_wrappers
• codec
• collections
• tikv_util
• file_system

They should be either published to crates.io or inlined all used functions/types.

After this change, these projects will not be part of tikv/tikv anymore. But they will still be part of release binaries.

Any thoughts?

[skyzh]

I think we should probably go toward this direction. But there're some more practical problems to solve.

How can we run CI for copr? Currently we rely on integration-copr-test to ensure it works (though it has been failing on main branch for months). Moving copr to a separate repo would make things harder, as we see them as standalone modules and may only run unit tests for them.

[BusyJay]

We still need to include it in TiKV release binaries, so CI may clone the transferred repository during compilation. And the new repo, perhaps named tidb-query, may work as an add-on. So CI can still be run on demand. Though I would suggest to run integration-copr-test in tidb-query repo instead of tikv repo.