refactor:remove repeated build beforeImage and afterImage in undo/bui…

[ForestLH]

What this PR does: refactor the architecture of build beforeImage and afterImage.

• [x] remove repeated build beforeImage and afterImage in undo/builder package
• [x] extract the public ExecContext logic of at's Executor into BaseContext and place it in the internal package.
• [x] add an abstract interface for build beforeImage and afterImage, in this way, databases can implement this interface, like MySQL, PostgreSQL.

But now its support MySQL only, other DBMS are left to support other tasks.

Which issue(s) this PR fixes:

Fixes #751