add semantic tokens for deprecated items

[xdBronch]

this lets things be rendered with a strikethrough without needing any diagnostics

it can be set in vscode settings like so

    "editor.semanticTokenColorCustomizations": {
        "rules": {
            "*.deprecated": { "fontStyle": "strikethrough" }
        }
    },

[ChayimFriedman2]

I'm not entirely sure, but I think I prefer to handle this for each variant in a common place instead of duplicating it all over, e.g. from the match over the definition return Option<AttrsWithOwner> as well, then check it after.

[xdBronch]

sure i think that makes sense, the places we handle it become a little cleaner

[ChayimFriedman2]

Thanks!