br: restore merge split ranges with small data

[Leavrth]

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]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[tiprow]

Hi @Leavrth. Thanks for your PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 78.29132% with 155 lines in your changes missing coverage. Please review.

Project coverage is 75.6804%. Comparing base (383643f) to head (760a4d0).
Report is 211 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #55104        +/-   ##
================================================
+ Coverage   72.7353%   75.6804%   +2.9451%     
================================================
  Files          1561       1583        +22     
  Lines        438868     457788     +18920     
================================================
+ Hits         319212     346456     +27244     
+ Misses        99960      90121      -9839     
- Partials      19696      21211      +1515     

Flag	Coverage Δ
integration	50.4036% <68.6274%> (?)
unit	71.7872% <56.0224%> (+0.0583%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9567% <ø> (ø)
parser	∅ <ø> (∅)
br	60.6760% <78.2913%> (+14.7993%)	⬆️

[Leavrth]

/retest

[tiprow]

@Leavrth: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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[Leavrth]

TODO: use defer

[ti-chi-bot]

PR needs rebase.

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[Leavrth]

This PR is split into these three PRs:

1. br: clean codes -- simplify the CreateTable stage #55274
2. br: clean codes -- restore tables #55519
3. br: restore merge split ranges with small data #55662