We don't support the complex expression keys in the rollup/cube, and we even will not report it if we have the complex group by keys, that will cause very confusing/incorrect result.

e.g. `SELECT key%100 FROM src GROUP BY key %100 with ROLLUP`

This PR adds an additional project during the analyzing for the complex GROUP BY keys, and that projection will be the child of `Expand`, so to `Expand`, the GROUP BY KEY are always the simple key(attribute names).

Author: Cheng Hao <hao.cheng@intel.com>

Closes #7343 from chenghao-intel/expand and squashes the following commits:

1ebbb59 [Cheng Hao] update the comment
827873f [Cheng Hao] update as feedback
34def69 [Cheng Hao] Add more unit test and comments
c695760 [Cheng Hao] fix bug of incorrect result for rollup