test(loader): Add tests for new loader integration handling

[mydea]

These are tests added for getsentry/sentry#47082

This should make sure that:

• If you do not add replay/browser tracing integrations, we add them for you
• If you add them, we do not overwrite them but use your own config
• If you add any other integrations, they are added in addition to replay/browser tracing

I also make sure we check the loader & integration bundles for ES5.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.94 KB (-0.01% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	65.44 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.49 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	57.88 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.1 KB (0%)
@sentry/browser - Webpack (minified)	68.84 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.12 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.9 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.5 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.73 KB (0%)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.89 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	38.85 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	63.78 KB (0%)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	56.82 KB (0%)