fix(browser): Wait for document 'complete' state before terminating pageload transaction

[lforst]

We have the theory that we are missing out on web vitals because we are still ending transactions too early.

This PR builds on #10215 where we started to delay the txn auto-finishing until the document is interactive. With the change in this PR we delay it even further until al dom resources have loaded.

We make the assumption that this is what users actually want.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	77.93 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.18 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	73.11 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	62.77 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.37 KB (-0.03% 🔽)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.27 KB (-0.04% 🔽)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.21 KB (0%)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.22 KB (0%)
@sentry/browser - Webpack (gzipped)	22.47 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	76.27 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.8 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.75 KB (-0.03% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.8 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	213.3 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.93 KB (-0.05% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	74.33 KB (0%)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.93 KB (-0.03% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.53 KB (-0.01% 🔽)
@sentry/react - Webpack (gzipped)	22.5 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.03 KB (-0.02% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	50.21 KB (-0.02% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	17.2 KB (0%)

[AbhiPrasad]

Let's add an integration test?