*: fix data race of Column.GeneratedExpr (#48888)

[ti-chi-bot]

This is an automated cherry-pick of #48888

What problem does this PR solve?

Issue Number: close #44919, close #48191.

Problem Summary:

What changed and how does it work?

Add Clone() and Internal() method for Column.GeneratedExpr field.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

  $ go test -race github.com/pingcap/tidb/pkg/ddl/ingest -test.run ^TestAddIndexIngestMultiSchemaChange$ --tags=intest
  ok      github.com/pingcap/tidb/pkg/ddl/ingest  3.772s
  

• 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

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@069631e). Click here to learn what that means.
The diff coverage is 64.2857%.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #48924   +/-   ##
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  Coverage               ?   72.7417%           
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  Files                  ?       1404           
  Lines                  ?     413078           
  Branches               ?          0           
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  Hits                   ?     300480           
  Misses                 ?      93051           
  Partials               ?      19547           

Flag	Coverage Δ
unit	72.7417% <64.2857%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.4224% <0.0000%> (?)

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-01 08:31:03.575993052 +0000 UTC m=+1640705.140290756: ☑️ agreed by hawkingrei.
• 2024-02-01 09:17:25.589625648 +0000 UTC m=+1643487.153923350: ☑️ agreed by zimulala.

[Benjamin2037]

LGTM

[Benjamin2037]

/retest

[Benjamin2037]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, hawkingrei, tangenta, zimulala

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Needs approval from an approver in each of these files:

• OWNERS [Benjamin2037,hawkingrei,tangenta,zimulala]
• br/pkg/lightning/OWNERS [Benjamin2037]
• pkg/ddl/OWNERS [Benjamin2037,tangenta,zimulala]
• pkg/table/OWNERS [Benjamin2037,tangenta,zimulala]

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[Benjamin2037]

/retest

[Benjamin2037]

/retest

[Benjamin2037]

/retest