fix: add support for trusted types CSP

[teemingc]

closes #7975

This PR:

• adds a validation error that guides the user to update their Svelte version when using the CSP directive require-trusted-types-for or trusted-types.
• uses a trusted policy to register the service worker when possible
• errors if the svelte policy name is not included when trusted-types is configured
• errors if the sveltekit policy name is not included when trusted-types is configured and a service worker exists and is automatically registered by us. We don't care if the user is registering the service worker on their own because then they can create their own trusted policy while doing so

Open questions

1. Should we automatically add svelte-trusted-html to trusted-types if require-trusted-types-for is in use?
   • This will cause any other trusted type policies to throw an error.
2. Or should we only add svelte-trusted-html when the user has trusted-types configured?
   • This means any trusted type policy is permitted on the page, which kind of defeats the purpose.
3. Or should we do nothing?
   • This means any trusted type policy is permitted on the page, which kind of defeats the purpose.
   • If the user has trusted-types configured but omitted svelte-trusted-html, they will have to discover the error message in the browser console logs, and figure out that they have to add the svelte trusted type to the config themselves.
4. Or should we error when the trusted-types config option isn't configured alongside the require-trusted-types-for option?
   • This will help teach users to add svelte-trusted-html themselves.
   • Could be kind of annoying and/or limiting.

---

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