Add a new trait to accept more types in the `Val`-helper functions (#20551)

# Objective

- Allow the `Val`-helper functions to accept more types besides just
`f32`

Fixes #20549

## Solution

- Adds a new trait that can be implemented for numbers
- That trait has a method that converts `self` to `f32`

## Testing

- I tested it using Rust's testing framework (although I didn't leave
the tests in, as I don't deem them important enough)

<details>
  <summary>Rust test</summary>

```rust
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_val_helpers_work() {
        let p = px(10_u8);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_u16);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_u32);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_u64);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_u128);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_i8);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_i16);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_i32);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_i64);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10_i128);
        assert_eq!(p, Val::Px(10.0));

        let p = px(10.3_f32);
        assert_eq!(p, Val::Px(10.3));

        let p = px(10.6_f64);
        assert_eq!(p, Val::Px(10.6));
    }
}
```
</details>

---

## Showcase

```rust
// Same as Val::Px(10.)
px(10);
px(10_u8);
px(10.0);
```