ENH: raise limit for completion number of columns and warn beyond
Hi,

Currently the user-completion (ipython "\<tab\>") on a dataframe with more than 100 columns will silently ignore some columns, letting an unaware user confused on whether data disapeared.

This is actually documented, and due to an arbitrary limit set to workaround a performance issue ( See #18587 )

Dataframe with more than 100 columns are quite common, so this can potentially affect and suprise many users. Therefore, I suggest to increase that limit to, say, 1000. In any case, it would probably be good to warn the user hitting that limit. 

The attached quickfix raises the limit to 1000 and adds a warning beyond. 
(Note that I didn't experience any completion latency increasing with the axis size, so I'm not sure whether this limit is still relevant in the first place).

