br: calculate the global checkpoint-ts of log-back task.

[joccau]

Signed-off-by: joccau zak.zhao@pingcap.com

What problem does this PR solve?

Issue Number: close #38776

Problem Summary:

What is changed and how it works?

To get global checkpoint-ts of log-back task, calculate ts from the different level( the store level, global level and storage level)

Check List

Tests

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

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth
• YuJuncen

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[joccau]

/merge

[ti-chi-bot]

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

Commit hash: 96eb444

[sre-bot]

TiDB MergeCI notify

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	24 min	Existing passed
idc-jenkins-ci/integration-cdc-test	🟢 all 38 tests passed	20 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	16 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	15 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	5 min 44 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	4 min 58 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	3 min 53 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 53 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	2 min 44 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed