lightning: fix id allocator base for double auto_increment field (#1178)

[ti-chi-bot]

This is an automated cherry-pick of #1178

What problem does this PR solve?

Fix the bug that lightning will got invalid auto_increment base if the corresponding auto_increment field is double/float.

[2021/06/05 13:37:03.227 +08:00] [INFO] [tidb.go:355] ["alter table auto_increment start"] [table=`db`.`table`] [auto_increment=4753151844738400257]

What is changed and how it works?

Check List

Tests

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

Code changes

Side effects

Related changes

Release note

• Fix the bug that lightning rebase wrong auto_increment base when the auto_increment field type is float or double.

[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• kennytm

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[3pointer]

/merge

[ti-chi-bot]

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

Commit hash: 0f065d7