ref(core): Rename Span class to SentrySpan

[mydea]

And stop exporting it from packages other than core.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	77.94 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.18 KB (0%)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	73.11 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	62.78 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.38 KB (0%)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.28 KB (0%)
@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 (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.8 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.75 KB (-0.02% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.8 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	213.33 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.95 KB (-0.02% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	74.33 KB (0%)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.93 KB (-0.02% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.53 KB (0%)
@sentry/react - Webpack (gzipped)	22.5 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.04 KB (0%)
@sentry/nextjs Client - Webpack (gzipped)	50.22 KB (0%)
@sentry-internal/feedback - Webpack (gzipped)	17.2 KB (0%)