ref(replay): Extract sticky session handling

[mydea]

Currently, a Session in replay receives stickySession as argument, and conditionally saves itself in its setters.

IMHO this responsibility is better placed outside of the session class. This also allows us to streamline the Session class quite a lot.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.57 KB (-0.02% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.59 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.36 KB (+0.01% 🔺)
@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)	45.99 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.44 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.88 KB (+0.02% 🔺)
@sentry/replay index.js	62 KB (-0.13% 🔽)
@sentry/replay - Webpack (gzipped + minified)	62.01 KB (-0.13% 🔽)
@sentry/replay - Webpack (minified)	199.35 KB (-0.25% 🔽)

[Lms24]

I think it's a good refactor because a) the actual saveSession logic wasn't in the class before so IMO it makes sense to separate it completely and b) this gets rid of the circular dependency we had between session.ts and saveSession.ts.