[VL] Support partial generate for UDTF

### Description

For generator that is an instance of `HiveGenericUDTF`, the `GenerateExec` can't be offloaded and therefore the plan will have a c2r and r2c. After the evaluation of `GenerateExec`, the number of rows may be several times more than that before the evaluation of `GenerateExec`. So we can implement `partial generate` to improve performance.

### Gluten version

None