feat(core): Deprecate getActiveTransaction() & scope.getTransaction()

[mydea]

A lot to refactor for us... but for now, let's deprecate this.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	76.49 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	67.88 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	61.5 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	32.13 KB (0%)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	30.7 KB (0%)
@sentry/browser - Webpack (gzipped)	22.07 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	74.1 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	65.75 KB (0%)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	31.93 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped)	23.76 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	206.52 KB (0%)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	96.4 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	70.93 KB (0%)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	34.89 KB (0%)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	68.25 KB (0%)
@sentry/react - Webpack (gzipped)	22.09 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	84.97 KB (0%)
@sentry/nextjs Client - Webpack (gzipped)	49.33 KB (0%)
@sentry-internal/feedback - Webpack (gzipped)	16.74 KB (0%)

[lforst]

christ this is gonna be the most painful one to clean up.