is_list_like() for to_excel, fixes #8188. 
closes #8188 

your comparison is going to be different as this is not a round-trippable format (e.g you will need to parse the return string and store it as a list in the expected frame).
- need an addition to the doc-string on the proposed conversion
- need a release note 
 Okay, I will try and add those soon. Sorry about the incorrect test, I'm still learning on this stuff. 
 @hunterowens you might want to check out the performance impact of this as well, given that it has to be called on every single value of every cell that gets written.
 @hunterowens working on this?
 closing pls reopen if/when updated
