vars to replace check_extra_args

[jdx]

I'm thinking we could do this:

linters = new {
    ["prettier"] = new builtins.Prettier {
      vars {
        ["check_extra_args"] = "--foo"
      }
    }
}

which would be defined in the builtin like this:

import "../hk.pkl"

class Prettier extends hk.Step {
    glob = new { "**/*.{js,jsx,ts,tsx,css,scss,less,html,json,jsonc,yaml,markdown,markdown.mdx,graphql,handlebars,svelte,astro,htmlangular}" }
    check = """prettier --check{{vars["check_extra_args"]}} {{ files }}"""
    fix = """prettier --write{{vars["fix_extra_args"]}} {{ files }}"""
}