Fix issue with formatting comment on labelled argument in uncurried mode

[cristianoc]

Fixes #6094

[cristianoc]

It was initially unclear why the fix was needed in the previous implementation. The issue occurred when the uncurried transformation wrapped the function with Function$ using the same location as the function itself, which seemed to interfere with the comment logic that processes the parse tree.

The current fix assigns a ghost location to Function$. This should not cause any issues, as long as type errors or other issues silently pass by it. However, if there are any real errors related to Function$ in the future, such as an accidental name change, the resulting error will not have a location.