feat(core): Update withScope to return callback return value

[mydea]

To align this with OpenTelemetry and make some things possible that are currently not easily doable without pushScope / popScope.

Noticed this because currently it's not easily possible to e.g. use withScope in places like this.

This should be backwards compatible because any code that previously relied on this returning void should still work.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	75.17 KB (-0.04% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	66.58 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	60.18 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.29 KB (-0.01% 🔽)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	29.89 KB (-0.08% 🔽)
@sentry/browser - Webpack (gzipped)	21.58 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	72.53 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	64.3 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	30.54 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped)	22.6 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	202.31 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	92.51 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	67.54 KB (+0.03% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	33.45 KB (0%)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	66.96 KB (-0.01% 🔽)
@sentry/react - Webpack (gzipped)	21.62 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	83.7 KB (0%)
@sentry/nextjs Client - Webpack (gzipped)	48.4 KB (-0.01% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	16.18 KB (-0.11% 🔽)

[mydea]

Noticed that linting may fail with this update - with the @typescript-eslint/no-floating-promises rule if you had withScope(async () => {}) without voiding/returning/using this, lint may complain. But I think we should still do it, otherwise a bunch of the pre-v8 refactors (getting rid of pushScope internally etc) will be impossible to do 😬

[mydea]

This actually shows how much better this is :D