Depends on the language parser recognising the definition, at least works for functions in C, C++ and Python on Linux, don't have other language sources immediately available and can't test windows.
The benefit a tooltip has over a table is that it expands to accommodate the size of the declaration (since declarations can be large). I'm not sure an expanded table is a good idea, it would use lots of the screen, but if somebody made a pull request with it controlled by a setting it could be evaluated.