[close #639] reduce lock granularity of RegionStoreClient and PDClient (#638)

[ti-srebot]

cherry-pick #638 to release-3.3
You can switch your code base to this Pull Request by using git-extras:

# In client-java repo:
git pr https://github.com/tikv/client-java/pull/642

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

git push git@github.com:ti-srebot/client-java.git pr/642:release-3.3-1b5edcd8ab8e

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Signed-off-by: iosmanthus myosmanthustree@gmail.com

What problem does this PR solve?

Issue Number: close #639

Problem Description:

This pull request tries to reduce the lock granularity of ReionStoreClient and PDClient, we might block the requests while under a heavy workload.

What is changed and how does it work?

1. Remove the synchronized keyword for RegionStoreBuilder.build, since the region cache's methods have already been synced.
2. Remove the synchronized keyword in PDClient's update leader logic, since the leader will be eventually updated to the latest one by the update leader scheduler.

Check List for Tests

This PR has been tested by at least one of the following methods:

• Unit test
• Integration test

Related changes

• Need to cherry-pick the release branch

[ti-srebot]

/run-all-tests

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-3.3@9a127af). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             release-3.3     #642   +/-   ##
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  Coverage               ?   34.78%           
  Complexity             ?     1433           
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  Files                  ?      278           
  Lines                  ?    17377           
  Branches               ?     1974           
==============================================
  Hits                   ?     6045           
  Misses                 ?    10722           
  Partials               ?      610           

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[iosmanthus]

LGTM