Macro based scalar function definitions make IDE harder to trace function usage

### Is your feature request related to a problem or challenge?

I'm revamping the planner in Comet for some recent changes happened in DataFusion, especially for scalar functions.

I found that a few built-in scalar functions are moved into module `expr_fn` with the approach with some macros.

One trouble with this approach is it is hard to trace how does these functions are used across DataFusion. At least in RustRover IDE, it cannot trace the function usage on these function defined by `export_functions` macro.

I'm not sure how do others deal with it?

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Inizia leggendo le definizioni delle funzioni scalari integrate nel modulo expr_fn e l’utilizzo della macro export_functions descritto nell’issue. Esamina come RustRover traccia queste funzioni e determina un approccio concreto; il lavoro è completato quando gli utilizzi delle funzioni in tutto DataFusion possono essere tracciati in modo affidabile nell’IDE.

Scritto dal modello di indicizzazione a partire dal testo della issue.