tracker(dm): respect CHARSET when build TableInfo (#4638)

[ti-chi-bot]

This is an automated cherry-pick of #4638

Signed-off-by: lance6716 lance6716@gmail.com

What problem does this PR solve?

Issue Number: close #4637

What is changed and how it works?

found that MockTableInfo will always use default charset and collation, BuildTableInfoFromAST is better

Check List

Tests

• Unit test
• Integration test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

Fix a bug that long varchar will report error of "Column length too big..."

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[lance6716]

/merge

[ti-chi-bot]

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

Commit hash: 7a69e15

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