Function Signature highlight as you type

[FourierTransformer]

Currently the function signature LSP method just shows the function signature when you type a (, but it can also highlight and identify where you are in the function signature.

An example of this working in Python: https://basedpyright.com/?typeCheckingMode=all&code=A4JwlgdgLgFAlEA

The lsp_formatter.tl likely needs to be updated a bit as well as the function signature method in misc_handlers.tl