discard the extended checksum part in row values

[zyguan]

What problem does this PR solve?

Issue Number: ref pingcap/tidb#42747

Problem Description:

Row values now may have extended checksums since pingcap/tidb#42859, so client-java need to discard these checksums on read.

What is changed and how does it work?

Do not copy the checksum part to RowV2.data. Actually the current implementation is ok since RowV2.data can be only accessed by RowV2.getData. This PR just makes it more safer.

[tidb-cloud-branching-dev]

The latest updates on TiDB Cloud Branch. Learn more about TiDB Cloud ↗︎

BranchName	ClusterID	Status	Updated
discard-row-checksum_739_5b77567	3059033	running	2023-04-24T06:34:36Z

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.76%. Comparing base (cb26d58) to head (eecfdcf).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
src/main/java/org/tikv/common/codec/RowV2.java	0.00%	6 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #739 +/- ##
============================================
- Coverage 37.93% 37.76% -0.18% + Complexity 1613 1603 -10 
============================================
Files 278 278 Lines 17517 17522 +5 Branches 1992 1994 +2 ============================================
- Hits 6645 6617 -28 - Misses 10208 10237 +29 - Partials 664 668 +4 

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[shiyuhang0]

roughly approve.
But will client-java return row with checksums col before this optimize？
checksum seems a feature of tidb and it does not exist in TiKV, which means it may not influence client-java. have you tested this pr locally?

.