ddl: refactor adjustColumnInfoInAddColumn for multi-schema change

[tangenta]

What problem does this PR solve?

Issue Number: ref #14766

Problem Summary:

Previously, onAddColumn assumes the newly adding column is at the end of TableInfo.Columns. This is not true anymore if we support multi-schema change: there may be several adding columns at the same time.

adjustColumnInfoInAddColumn should support moving any column.

What is changed and how it works?

Check List

Tests

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

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Defined2014
• zimulala

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/e4929e71235661c3085923e7c889d7e4ac453476

[zimulala]

Please run schrddl test manually

Rest LGTM

[tangenta]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 061aebb

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