This pr makes three changes to the display of complex types：
1. NULL value in complex types refers to being displayed as `null`, not `NULL`
2. struct type is displayed as "column_name": column_value
3. Time types such as `datetime` and `date`, are displayed with double quotes in complex types. like
`{1, "2023-10-26 12:12:12"}`
This pr also do a code refactor:
1. nesting_level is set to a member variable of the `DataTypeSerDe`, rather than a parameter in methods.
What's more, this pr fix a bug that fileSize is not correct, introduced by this pr: #25854
fix shrink char column in map/struct
before we has char with specific length defined in map or struct field
we select map or struct , the char column in which one has been padding if we just insert less than specific length chars
but in mysql here just show inserted chars not padding specific length chars
---------
Co-authored-by: yiguolei <676222867@qq.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
