Pass visitor to visit_number! macro

[Aaron1011]

In Rust, variable identifiers in a macro_rules! body are resolved
in the scope of tht body - they cannot see through to the caller's body.
For example, the following code errors:

macro_rules! weird_ident {
    () => { my_ident; }
}

fn main() {
    let my_ident = 1;
    weird_ident!();
}

However, due to a compiler bug (rust-lang/rust#43081),
this kind of code current compiles when a procedural macro is invoked by
a macro_rules! macro. Eventually, this will cause a compilation error.

In the visit_number! macro, you're currently writing an expression
involving visitor, and passing it to a procedural macro (paste!).
However, visitor comes from the body of the caller of visit_number!,
so this code will stop compiling once the compiler bug is fixed.

Fortunately, the identifier of visitor can be passed into
visit_number!. This modified code will with the current version of
Rust, as well as future version that causes the old code into an error.

Feel free to ask me about any questions you may have. For more details,
see rust-lang/rust#72622

[ilyvion]

Ah, you're the one who accidentally tagged all those people by accident. 😄 Thank you for finding and fixing this issue in my code. I honestly never expected a pull request to this repo, much less due to a change to the Rust compiler, but I appreciate just being handed the fix. 👍

[Aaron1011]

@alexschrod: Could you make a new point release containing this fix? When rust-lang/rust#73084 is merged, this bug will be exposed.