Returns a list of symbols (functions, classes, variables, etc.) defined in the specified file.
Only the variabels defined at the file level are included.
The returned positions point to the start of the symbol’s identifier.
e.g. for User on line 0 of src/main.py:
0: class User:
_________^
1: def __init__(self, name, age):
2: self.name = name
3: self.age = age