feat: deal with the unique field migrator

[Icemap]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

To handle the AlterColumn(), because TiDB can't change column constraint.

User Case Description

[jinzhu]

Maybe we can add a DontSupportRenameColumnUnique field to Config, and during initialize, set it to true if dialector.ServerVersion contains TiDB?

And in the AlterColumn method just remove the Unique from the FullDataType if DontSupportRenameColumnUnique is true?

[Icemap]

Sure. But it would be taken time. Because I have a little bit thing need to develop from the company. I'll come back here maybe next week.

[Icemap]

Maybe we can add a DontSupportRenameColumnUnique field to Config, and during initialize, set it to true if dialector.ServerVersion contains TiDB?

And in the AlterColumn method just remove the Unique from the FullDataType if DontSupportRenameColumnUnique is true?

Hi @jinzhu, I already make it done. PTAL again.

[Icemap]

Continue for go-gorm/gorm#6014