[Bug] Fix fe meta version problem, make drop meta check code easy to read and add doc content for drop meta check

[caiconghui]

Proposed changes

This PR is mainly do three things:

1. Fix fe meta version bug introduced by Support check committed txns before catalog drop meta, like db, table, partition etc #4029 , when fix conflict with [Feature][Meta]Update/Read/Write VisibleVersionTime for Partition#4076 #4086
2. Make drop check code easy to read
3. Add doc content for drop meta check

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• Documentation Update (if none of the other choices apply)
• Code refactor (Modify the code structure, format the code, etc...)

Checklist

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• I have create an issue on #ISSUE [Bug] Wrong fe meta version check for DropDbInfo and doc content for drop meta check is needed #4204 , and have described the bug/feature there in detail
• Compiling and unit tests pass locally with my changes

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

[morningman]

LGTM