Fix incorrect `Parameter` range for `*args` and `**kwargs` (#10283)
## Summary
Fix #10282
This PR updates the Python grammar to include the `*` character in
`*args` `**kwargs` in the range of the `Parameter`
```
def f(*args, **kwargs): pass
# ~~~~ ~~~~~~ <-- range before the PR
# ^^^^^ ^^^^^^^^ <-- range after
```
The invalid syntax `def f(*, **kwargs): ...` is also now correctly
reported.
## Test Plan
Test cases were added to `function.rs`.