Recognize function pointers as functions (`Fn("foo")` => `fn foo(...)`)

@tamasfe   I have a new drop in the repo that implements a convenient shorthand to create function pointers.

```rust
fn fib(a) { ... }

let fp = Fn("fib");    // original syntax

let fp = fib;        // new syntax, de-sugars to Fn("fib")
```

The LSP may need to be aware of this, as it might flag `fib` as an undeclared variable.
