ref(replay): Export WINDOW within Replay instead of importing it from Browser

[Lms24]

In preparation of generating CDN bundles, this PR copies the WINDOW constant declaration from @sentry/browser to the Replay package and updates the imports to use the package-internal version of WINDOW. This has two advantages:

• When building CDN bundles, we don't bundle contents from @sentry/browser anymore. This previously caused the generated bundles to not work correctly and it unnecessarily increased bundle size
• By not importing anything from @sentry/browser we avoid a circular dependency one we export the Replay integration from the Browser SDK.

ref #6362

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.57 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	60.59 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.36 KB (+0.03% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	54.15 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.12 KB (0%)
@sentry/browser - Webpack (minified)	65.75 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.14 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	45.97 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.42 KB (+0.01% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.85 KB (+0.02% 🔺)
@sentry/replay index.js	37.08 KB (-0.01% 🔽)
@sentry/replay - Webpack (gzipped + minified)	37.05 KB (-0.01% 🔽)
@sentry/replay - Webpack (minified)	124.54 KB (-0.09% 🔽)