ref(core): move beforeEnvelope to client

[JonasBa]

I was wrong in moving beforeEnvelope to transport constructor as no client is bound when transport is created, hence client && client.emit will fail...

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.53 KB (+0.21% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	63.85 KB (+0.46% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.19 KB (+0.42% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	56.92 KB (+0.52% 🔺)
@sentry/browser - Webpack (gzipped + minified)	21.66 KB (-0.1% 🔽)
@sentry/browser - Webpack (minified)	72.12 KB (-0.07% 🔽)
@sentry/react - Webpack (gzipped + minified)	21.7 KB (-0.1% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	52.02 KB (-0.08% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	33.76 KB (-0.06% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.13 KB (-0.05% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.23 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	38.28 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	62.44 KB (-0.02% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	55.99 KB (+0.85% 🔺)