*: add some comments to exported function, part 3 of enable revive.exported

[okJiang]

What problem does this PR solve?

Issue Number: Ref #8458

What is changed and how does it work?

add comments for exported and update some exported-function to unexported

Check List

Tests

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

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[codecov]

Codecov Report

Attention: Patch coverage is 79.67480% with 25 lines in your changes missing coverage. Please review.

Project coverage is 77.40%. Comparing base (7741924) to head (fa57a7c).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8507   +/-   ##
=======================================
  Coverage   77.40%   77.40%           
=======================================
  Files         472      472           
  Lines       61800    61828   +28     
=======================================
+ Hits        47838    47860   +22     
- Misses      10395    10400    +5     
- Partials     3567     3568    +1     

Flag	Coverage Δ
unittests	77.40% <79.67%> (+<0.01%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HuSharp, rleungx

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• OWNERS [HuSharp,rleungx]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-09 08:23:34.618995937 +0000 UTC m=+599544.486095024: ☑️ agreed by rleungx.
• 2024-08-09 08:52:18.290604158 +0000 UTC m=+601268.157703247: ☑️ agreed by HuSharp.