br: restore merge split ranges with small data (#55662)

[ti-chi-bot]

This is an automated cherry-pick of #55662

What problem does this PR solve?

Issue Number: close #53532

Problem Summary:
br restore splits too many regions if there are too many small tables whose data size is less than region size.

What changed and how does it work?

ignore some keys to split less regions
Due to tikv/tikv#17278, BR needs merge the generated SSTMeta at the same region into one Ingest request.

Check List

Tests

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

  • I checked and no code files have been changed.

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]

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/mysql-test	5a34192	link	true	/test mysql-test
idc-jenkins-ci-tidb/check_dev	5a34192	link	true	/test check-dev
idc-jenkins-ci-tidb/build	5a34192	link	true	/test build
idc-jenkins-ci-tidb/check_dev_2	5a34192	link	true	/test check-dev2
idc-jenkins-ci-tidb/unit-test	5a34192	link	true	/test unit-test

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[BornChanger]

it's a new feature, not ready to cherry-pick to 7.5