feat(replay): Capture fetch body size for replay events

[mydea]

This adjusts the replay request body capturing to capture the fetch body size if no Content-Length header is present.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.44 KB (+0.01% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	63.52 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.13 KB (+0.01% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	56.57 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.59 KB (0%)
@sentry/browser - Webpack (minified)	71.65 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.61 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	51.85 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.77 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.08 KB (0%)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.3 KB (+0.2% 🔺)
@sentry/replay - Webpack (gzipped + minified)	38.36 KB (+0.21% 🔺)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	62.49 KB (+0.15% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	56.03 KB (+0.16% 🔺)

[billyvg]

Tested this on my local Sentry and it works - though I do want to note that the sizes are slightly off from the browser which shows the size over the network (which I assume is smaller due to compression). Thoughts on the best way to inform users on the UI here since we display the "resource size" that is on the tooltip vs "transferred over the network".

[mydea]

Tested this on my local Sentry and it works - though I do want to note that the sizes are slightly off from the browser which shows the size over the network (which I assume is smaller due to compression). Thoughts on the best way to inform users on the UI here since we display the "resource size" that is on the tooltip vs "transferred over the network".

It may also differ because I guess the network tab includes header etc. data into the size, maybe? But even if not it could def. be slightly different, hard to say how exactly that is calculated..!