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

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	5aec663	link	true	/test check-dev2
idc-jenkins-ci-tidb/build	5aec663	link	true	/test build
idc-jenkins-ci-tidb/check_dev	5aec663	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	5aec663	link	true	/test unit-test
idc-jenkins-ci-tidb/mysql-test	5aec663	link	true	/test mysql-test

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