Add static modifier to static variables

[maxwase]

Fixes #16894

It seems that there is a name collision between SymbolKind::Static and HlMod::Static resulting in a wired looking test diff (static mutable static unsafe), that's why I decided to rename SymbolKind::Static. I don't think that any of these are exposed to a user, however, not fully sure, I was not able to break my configuration with either of these name changes.

Tested with the following config static colors configuration:

    "editor.semanticTokenColorCustomizations": {
        "enabled": true,
        "rules": {
            "variable": "#FFFFFF",
            "variable.static": {
                "bold": true,
                "foreground": "#cc711d",
            },
            "variable.constant": {
                "bold": true,
                "foreground": "#F0F080",
            },
        }
    }

// semantic token type : modifiers

// variable : declaration constant
const A: u32 = 0;
// variable : declaration static
static B: u32 = 0;

fn foo() {
    // variable : declaration
    let _c = 0;
}

[Veykril]

The name collision is fine. I remove the use of the static modifier for static items because I assumed they are used for static members usually (think of static methods in languages like java). It felt somewhat wrong to me to use it for static (as in the item) but arguably its not clear what it should be used for as the LSP spec (given its a standard modifiers) doesn't specify it.

[maxwase]

@Veykril I see your point, however I think it is probably ok to have it here, at least for the sake of diversification, without it there is no way to semantically distinguish those

[Veykril]

I'm still not too convinced by this being used for static items 😅 I opened #17074 which will add it as an item type instead (and const as well) as that seems more correct to me