Rewrite natvis description for HashMap to improve the visualization of key-value pairs in WinDbg

[nanguye2496]

The natvis description of Rust HashMap contains this line:

<Item Name="{((tuple&lt;$T1, $T2&gt;*)base.table.ctrl.pointer)[-(i + 1)].__0}">((tuple&lt;$T1, $T2&gt;*)base.table.ctrl.pointer)[-(i + 1)].__1</Item>

WinDbg's natvis executor fails to cast base.table.ctrl.pointer to tuple<$T1, $T2>*, leading to this issue rust-lang#82674. The cause of this failure comes from WinDbg's syntax parser, which adds a whitespace between $T1 and $T2 after substituting them by the corresponding parametric types. While waiting for a fix from WinDbg side, I propose this work-around.

For this program:

use std::fmt;

#[derive(PartialEq, Eq, Hash)]
struct Student {
    name: String,
    country: String,
}

impl fmt::Display for Student {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.name, self.country)
    }
}

fn main() {
    use std::collections::HashMap;
    let mut map = HashMap::new();
    let s1 = Student { name: String::from("Nam"), country: String::from("UK") };
    let s2 = Student { name: String::from("Alex"), country: String::from("US")};
    map.insert(s1, 10);
    map.insert(s2, 8);
    for (k,v) in map.iter() {
        println!("{}, {}", k, v);
    }
}

Here is the HashMap visualization before the fix:

Here is the HashMap visualization after the fix:

[nanguye2496]

We should display each key-value pair as a tuple instead of having the key as the item name to allow developers to examine HashMap keys of user-defined types in WinDbg.