feat(core): Deprecate Transaction.getDynamicSamplingContext in favour of getDynamicSamplingContextFromSpan

[Lms24]

This PR deprecates Transaction.getDynamicSamplingContext and introduces its direct replacement, a top-level utility function. Note that IMO this only is an intermediate step we should take to rework how we generate and handle the DSC creation. More details in #10095

Used various new APIs like spanToJSON and spanIsSampled. Observed that a slight behavioural change is, that isSpanSampled always returns a boolean while span.sampled could also be undefined. Considering integration tests still pass, I'd say this is fine.

Added new tests for the top level helper and left the older ones in place to still cover transaction.getDSC.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	76.98 KB (+0.13% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	68.36 KB (+0.17% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	61.99 KB (+0.19% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	32.38 KB (+0.31% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	30.98 KB (+0.79% 🔺)
@sentry/browser - Webpack (gzipped)	22.31 KB (+0.96% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	74.61 KB (+0.06% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	66.26 KB (+0.09% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	32.07 KB (+0.11% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	23.9 KB (+0.66% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	208.7 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	96.75 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	71.35 KB (+0.57% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	35.04 KB (+0.13% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	68.72 KB (+0.14% 🔺)
@sentry/react - Webpack (gzipped)	22.35 KB (+1% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	85.37 KB (+0.02% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	49.5 KB (+0.05% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	17.01 KB (+1.53% 🔺)