feat: remove SvelteKit specific handling

[bluwy]

Per changeset:

Remove internal SvelteKit specific handling

• Disallow kit prop in inline options
• Remove default hydratable: true option for SvelteKit
• Inspector code mounts on /@vite/client to be framework agnostic

Re no1, I'm not sure how we're using that today, but seems safe to me to remove the runtime validation for it.

Re no2, SvelteKit has set it by itself for quite a while now: https://github.com/sveltejs/kit/blob/fb68c253a59402df2b2b1b5db7a54fad504cdd32/packages/kit/src/exports/vite/index.js#L136

Re no3, this removes the need for the inspector.appendTo option so we don't need kit specific handling for it. Makes way for #631

[bluwy]

Dynamic import since the Inspector.svelte would rely on /@vite/client too, and it otherwise would cause an import loop and a runtime ReferenceError.

[dominikg]

the kit option and setting hydratable: true have been remnants for older versions of sveltekit.
Does removing them make this a breaking change?

Technically applications on older versions of kit can't update to newer v-p-s until they also update kit. But given that v-p-s is a dependency of kit and kit had a critical advisory that urged people to update to a version that is compatible, we could assume that updating v-p-s without also updating kit is not something we expect anyone to do?

[dominikg]

Older version above refers to sveltekit less than 1.0.0-beta.576. Anyone still using that should have updating to 1.0 as their first priority.