This PR is mainly do three things:
1. Fix fe meta version bug introduced by #4029 , when fix conflict with #4086
2. Make drop check code easy to read
3. Add doc content for drop meta check
[Bug]Fix some schema change not work right
This CL mainly fix some schema change to varchar type not work right
because forget to logic check && Add ConvertTypeResolver to add
supported convert type in order to avoid forget logic check
