feat(loader): Ensure default integrations are added & work for performance

[mydea]

This re-implements parts of the reverted #46447.

This updates the loader script to:

• Ensure we add the necessary integrations (Replay & BrowserTracing)
• Ensure the onerror/onunhandledrejection handlers of the loader & the JS SDK do not interfer (SDK-side fix for this: fix(loader): Ensure JS loader works with tracing & add tests sentry-javascript#7662)
• Ensure init is called before other methods, so e.g. captureException etc. will only be called afterwards

The other part is #46994 - this kind-of depends on this as without this the integrations will not be added (as the sample rates are not set). However they are only indirectly linked and can be merged/deployed separately.

Verification steps

• I verified both the min & and full loader script generated are ES5 compliant with es-check
• Tried in a local test app with the min & full loader script, both without performance/replay, as well as with them.
• I put the generated min. loader script into the JS SDK integration tests

[github-actions]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[AbhiPrasad]

Nothing seems to break when I ran in a local app! Let's