fix(otel): Set trace context via Otel Span instead of Sentry span

[AbhiPrasad]

ref: #6713

Since the SENTRY_SPAN_PROCESSOR_MAP can be empty due to the transaction/span already finishing after the event processor was triggered (due to async event processors), we instead rely only on the OpenTelemetry context to determine the active span.

The product uses trace_id and span_id to associate errors to transactions, so that's what we've kept.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.84 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	61.46 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.62 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.38 KB (0%)
@sentry/browser - Webpack (minified)	66.55 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.4 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.63 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.82 KB (+0.02% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.25 KB (-0.02% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.05 KB (-0.01% 🔽)
@sentry/replay - Webpack (gzipped + minified)	38.3 KB (0%)