ref(types): Use intersections instead of extend in envelope types

[AbhiPrasad]

Remove the usage of extend so that we don't eliminate the base envelope types.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.47 KB (-0.02% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.16 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.06 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	53.08 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	19.85 KB (0%)
@sentry/browser - Webpack (minified)	64.49 KB (0%)
@sentry/react - Webpack (gzipped + minified)	19.88 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	44.73 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.93 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.33 KB (-0.01% 🔽)