ref(sveltekit): Handle SvelteKit-generated spans in sentryHandle

[Lms24]

(This is still WIP and for now a conglomerate of changes)

If Kit tracing is used:

• Don't start a span if the kit request event signals that Sveltekit emits its own spans
• Don't emit httpIntegration incoming request span (kit or our handler take care of that)
• Process kit-emitted spans to include sentry op and origin
• Change name of root span to Sentry-esque http.server name conventions
  • store original name as sveltekit.tracing.original_name attribute
• We still isolate the request in addition and this works correctly

Build time adjustments

• Read tracing config from svelte.config.js
• Inject config into hooks.server.ts and instrumentation.server.ts
• Use this information at runtime to determine which integration to add (how)
• Make sure to always inject this value, independently of source maps config

Misc

• Add tests for span processing
• Add tests for buildtime tracing config functionality
• Add tests for runtime tracing config functionality
• Add e2e test app with full tracing functionality enabled
• Add e2e test app only with instrumentation but not tracing enabled

Maybe/follow-up

• Add build time or runtime log message to instruct users to use the new feature if we detect they don't yet

see sveltejs/kit#13899

ref #16982