Add types for `fetchpriority` on link and script elements

[oscarhermoso]

Describe the problem

Encountering red squiggles on fetchpriority, even though it's a valid attribute

It's annoying in this context because there's no way to suppress the error without applying // @ts-nocheck to the whole file (please correct me if I'm wrong)

<svelte:head>
    <script
        src="https://challenges.cloudflare.com/turnstile/v0/api.js?render=explicit"
        async
        on:load={() => {
            script_loaded = true;
        }}
        fetchpriority="low"></script>
<!--    ^^^^^^^^^^^^^^ 
        Object literal may only specify known properties, and '"fetchpriority"' does not 
        exist in type 'HTMLProps<"script", HTMLAttributes<any>>'.js(2353) -->
</svelte:head>

Describe the proposed solution

Add type support for the fetchpriority attribute on HTMLScriptElement. May as well add it for HTMLLinkElement while we are in the space too.

(Support for HTMLImageElement was already added here)

Browser support is solid, except for FireFox 🙂

Importance

nice to have

[dummdidumm]

fixes by #10390