ref(core): Always use a (default) ACS

[mydea]

Small refactor to ensure we always use a default async context strategy, making the default behavior more explicit.

This will (hopefully) make it easier to encapsulate this going forward.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	77.82 KB (+0.04% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.06 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	72.99 KB (+0.03% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	62.67 KB (+0.03% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.25 KB (+0.05% 🔺)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.15 KB (+0.05% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.16 KB (-0.02% 🔽)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.16 KB (-0.01% 🔽)
@sentry/browser - Webpack (gzipped)	22.43 KB (-0.04% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	76.1 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.61 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.58 KB (-0.06% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.69 KB (-0.05% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	212.82 KB (-0.04% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.45 KB (-0.07% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	73.96 KB (-0.09% 🔽)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.82 KB (-0.14% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.43 KB (+0.04% 🔺)
@sentry/react - Webpack (gzipped)	22.45 KB (-0.06% 🔽)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.09 KB (+0.01% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	50.36 KB (-0.01% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	17.12 KB (+0.04% 🔺)