Allow creating colorized things in const context

[blt-r]

We still cant put conts fn in impl Trait, so we can't mark methods of OwoColorize as const. But const_fn_trait_bound is already stable. Which means that we can allow creating FgColorDisplay (and others) in const context.

For example, like this:

impl<'a, C: Color, T> FgColorDisplay<'a, C, T> {
    pub const fn new(thing: &'a T) -> Self {
        Self(thing, PhantomData)
    }
}

#[test]
fn const_fg_color_display() {
    const YELLOW_FISH: FgColorDisplay<'static, Yellow, &'static str> = FgColorDisplay::new(&"><>");

    assert_eq!("\u{1b}[33m><>\u{1b}[39m", YELLOW_FISH.to_string())
}

I personally think having colorized constants is pretty useful (I created this issue because I wanted to do that, but found out, that I can't). So maybe we can add support for that in some form or another?

[jam1garner]

I will try to look into that as I definitely understand the desire. At minimum as trait const fns continue along more it'll definitely be better supported