Forget it. No-can-do in the Arduino Kiddie-IDE. You may want to check out Eclipse / Sloeber, that's what I use. I can't imagine doing serious code development in Arduino.
I understand that there is at least one other product with similar capabilities. Sorry, don't have a link.
I understand that there is at least one other product with similar capabilities.
Nearly ALL of the "pro" IDEs have this sort of feature. Even VIM and EMACS (via "tags.")
It's just one of the things that the Arduino IDE has left out.
Even if you choose not to use a non-Arduino IDE for working on Arduino projects, it can still be useful to use one for browsing the Arduino Core and Libraries...