Generate additional function parameters from function call

let's say we have the following code:

fn foo(x: i32) { ... }

I now want to add a second argument and add the parameter to the signature automatically, via assist.

foo(5, "bar");

resulting in this:

fn foo(x: i32, arg: &str) { ... }

This is somewhat similar to the assist to generate a new function based on a function call, but instead updating the signature of an existing function.
This would be especially useful when using more complex types that can be inferred.

Start from the existing assist that generates a new function from a function call, then trace how it identifies the called function and inferred argument types. Add the corresponding behavior for an existing function signature, and run the relevant assist tests to verify that the new parameter and type are generated correctly.