lightning: fix uuid panic when expression index enabled (#44516)

[ti-chi-bot]

This is an automated cherry-pick of #44516

What problem does this PR solve?

Issue Number: close #44497

Problem Summary:

What is changed and how it works?

Add e.SessionCtx.Vars.TxnCtx when getting default value for column with default expression.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  manually load data with uuid and it works.

Side effects

• None

Documentation

• None

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

lightning: fix the problem that lightning crashes when target table has a column whose default value is uuid

[lichunzhu]

/lgtm

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, lichunzhu

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-07-12 09:54:08.38015944 +0000 UTC m=+498540.150498138: ☑️ agreed by lichunzhu.
• 2023-07-12 09:55:55.766294131 +0000 UTC m=+498647.536632844: ☑️ agreed by lance6716.

[lichunzhu]

/test all

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/test all

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[lichunzhu]

/test check-dev2

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/test check-dev2

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