gcworker: fix gc miss locks when region merged during scanning & resolving locks (#22252)

[ti-srebot]

cherry-pick #22252 to release-3.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr 550915918

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/550915918:ti-srebot:release-3.0-bedd599e06c6-009f8c5c9568

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Signed-off-by: lysu sulifx@gmail.com

What problem does this PR solve?

Issue Number: close #22245

Problem Summary:

just as TestResolveLockRangeMeetRegionEnlargeCausedByRegionMerge

1. region1 with lock1, lock2 and region2 with lock3, lock4
2. gc scan region1 and get lock1, lock2
3. region2 merged into region1(so now region1 will have lock1, lock2, lock3, lock4)
4. gc retry to resolve lock1/lock2 but meet EpochNotMatchError caused by region merge
5. but due to gc_worker: reduce GC scan locks when meeting region cache miss #18385's bug, it doesn't re-scan region1 and thinking all locks in region1 has be resolved after resolve lock1, lock2
6. continue resolve lock after new region1's endKey and miss lock3, lock4 which merged from old region2

What is changed and how it works?

What's Changed, How it Works:

we need re-scan region's lock when found merged region's EndKey 's larger than origional region's EndKey

and we no need to re-scan lock when region has be splitted or region's EndKey has no change

Related changes

• Need to cherry-pick to the release branch 3.0, 4.0, 5.1

Check List

Tests

• Unit test

Side effects

• n/a

Release note

• Fix gc miss locks when region merged during scanning & resolving locks

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This change is 

[ti-srebot]

/run-all-tests

[ti-srebot]

@lysu you're already a collaborator in bot's repo.

[jackysp]

LGTM

[jackysp]

/merge

[ti-srebot]

/run-all-tests