feat(sveltekit): Auto-instrument universal and server load functions

[Lms24]

This PR adds auto-wrapping of load functions in page(.server).(ts|js) files to the SvelteKit SDK.

API

API wise, this is not a breaking change for users, as internally, we just add an additional plugin which is returned by the sentrySvelteKit plugin factory function. However, users can add new options to the factory functions, to control auto-wrapping:

sentrySvelteKit({
  autoInstrument: true, // false to disable entirely
  // or
  autoInstrument: {
    load: true,
    serverLoad: false,
  },
  // other options...
  autoUploadSourceMaps: false,
  debug: true,
})

Methodology

After trying a lot of options to bundle the original page module with a Sentry wrapper template (i.e. proxy loader in NextJS), I pivoted to modify the AST directly. The reason is that every time we touched source map generation, the resulting server source maps would no longer point to the original +page.ts/js files, causing broken source maps.
I believe this is a bug in the SvelteKit build process but I didn't find a way to work around this. Therefore, I suggest we go with the AST-based approach for now and revisit later if necessary.

I'm not too happy with the current approach because the fact that we can't touch the source maps also means, our AST wrapping can't modify the file content arbitrarily. We have to preserve the original location (at least the line) where the declaration of the load function was.

This PR also adds various tests for different kinds of load exports to ensure we handle them correctly.

closes #7940

[Lms24]

Draft, as I just had an idea. Will mark as ready for review once I verified it.

[Lms24]

Closing in favour of #7994