In my somewhat arrogant opinion, if you're navigating based on file name, you need a better IDE 🙂

How would you navigate to a file with only top level functions (like extensions) without any class inside the file? In IntelliJ or Android Studio I only managed to open it CMD+SHIFT+F and enter the file name.

you can search for the specific function with CMD-ALT-O, but I agree that if you want to find the group of extensions you often have to search by filename

By usage generally. If I'm in a file where I'm using the function and want to navigate to it, I use ctrl-click. If I'm in a file where I want to use it, I scroll from source and grab it (that assumes the files are close together, which is how I prefer to organize).