Apply Titan related changes

[v01dstar]

1. Making Statistics extensible, this is a cherry-pick of 7c6dcaa496564ec49cb1a135cfbf9e0a22cb31c5. In addition to the original PR, this new one also instantiate StatisticsImpl template at the end of statistics.cc to resolve visibility issues in tests
2. Add copy constructor to ColumnFamilyHandle, this is a prerequisite of https://github.com/tikv/titan/pull/298
3. Reassign ValueType::0x11 to kTypeTitanBlobIndex, and create a new kTypeBlobIndex (RocksDB native blob index) at 0x18, so that Titan blob index can be distinguished from RocksDB's native blob index, thus won't get mistakenly parsed by RocksDB and cause panic. Existing Titan instances don't need to migrate.

In the future, we need to merge this with #390 , attaching #390 description here:

• Reassign ValueType 0x10 to kTypeTitanColumnFamilyBlobIndex and 0x11 to kTypeTitanBlobIndex, and add WriteBatchInternal::PutTitanBlobIndex() for Titan to use.
• Move StatisticsImpl implementation from statistics.cc to statistics_impl.h. Template code should be in header files instead of cc files, otherwise, there will be undefined symbol error while linking.

Maintainer's note: When upgrading RocksDB in the future, we need to check all the occurrence of kTypeBlobIndex and kTypeColumnFamilyBlobIndex (for blob indices in non-default cf) in RocksDB's repo, and add kTypeTitanBlobIndex and kTypeTitanColumnFamilyBlobIndex accordingly. Anywhere kTypeColumnFamilyBlobIndex exists, we need to add kTypeTitanColumnFamilyBlobIndex, where kTypeBlobIndex exists, we need to add kTypeTitanBlobIndex.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Connor1996, glorv, LykxSassinator

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tikv/rocksdb/blob/8.10.tikv/OWNERS)~~ [Connor1996,LykxSassinator,glorv] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-09-30 09:00:19.622230151 +0000 UTC m=+258975.042443175: :ballot_box_with_check: agreed by Connor1996.
• 2024-09-30 09:02:01.344013559 +0000 UTC m=+259076.764226571: :ballot_box_with_check: agreed by LykxSassinator.
• 2024-09-30 23:26:32.311899715 +0000 UTC m=+310947.732112728: :heavy_multiplication_x::repeat: reset by v01dstar.

[ti-chi-bot[bot]]

New changes are detected. LGTM label has been removed.