*: refactor and fix the usages of DecodeIndexKV for clustered index

[tangenta]

What problem does this PR solve?

Problem Summary: Fix #23106.

In the process of the work "remove alter-primary-key configuration", I found TestAddIndex5 should test the clustered index case but it doesn't because the config alter-primary-key is enabled.

For details, see #23106.

What is changed and how it works?

What's Changed:

Bugfix:

• checkHandleExists: fix the comparison of the handle.
• (c *indexIter) Next(): fix handle decoding.

Test:

• *: Set the config correctly.

Refactor:

• decodeRestoredValuesV5: reduce the memory allocation, improve the readability.
• BuildRowcodecColInfoForIndexColumns: extract the process of building []rowcodec.ColumnInfo from index columns into a separated function.

Related changes

NA

Check List

Tests

• Unit test
• Integration test

Side effects

NA

Release note

• No release note

[wjhuang2016]

/lgtm

[wjhuang2016]

/run-check_dev_2 tikv=pr/9182

[coocood]

/run-all-tests

[wjhuang2016]

/run-all-tests

[tangenta]

[2021-03-09T11:04:53.261Z] FAIL: 2pc_test.go:735: testCommitterSuite.TestElapsedTTL
[2021-03-09T11:04:53.261Z] 
[2021-03-09T11:04:53.261Z] 2pc_test.go:749:
[2021-03-09T11:04:53.261Z]     c.Assert(lockInfo.LockTtl-atomic.LoadUint64(&ManagedLockTTL), Less, uint64(150))
[2021-03-09T11:04:53.262Z] ... compare_one uint64 = 0x97
[2021-03-09T11:04:53.262Z] ... compare_two uint64 = 0x96

/run-unit-test

[coocood]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• coocood
• wjhuang2016

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[coocood]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 9518be9

[tangenta]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e13700f

[coocood]

/run-unit-test

[ti-chi-bot]

@tangenta: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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