feat(core): Deprecate span name and description

[mydea]

Instead, users should use spanToJSON(span).description.

In reality, users should mostly not actually need this - most usages are internal things, or tests, right now.

While at this, I also updated the TraceContext type to not have a description. This started failing in a bunch of tests, because while in theory the trace context has a description field, in praxis we always used to set description to undefined for transactions, leading to this never being set. The work in this PR unifies the name/description handling between span and transaction, which lead to description not being undefined for transactions anymore, leading to this actually showing up in the trace context.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	76.49 KB (+0.36% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	67.88 KB (+0.43% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	61.5 KB (+0.48% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	32.13 KB (+0.9% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	30.7 KB (+0.51% 🔺)
@sentry/browser - Webpack (gzipped)	22.07 KB (+0.69% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	74.1 KB (+0.38% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	65.75 KB (+0.42% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	31.93 KB (+0.88% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	23.76 KB (+0.81% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	206.52 KB (+0.6% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	96.4 KB (+1.28% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	70.93 KB (+1.31% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	34.89 KB (+0.87% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	68.25 KB (+0.43% 🔺)
@sentry/react - Webpack (gzipped)	22.09 KB (+0.65% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	84.97 KB (+0.33% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	49.33 KB (+0.61% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	16.74 KB (+0.97% 🔺)

[mydea]

Updated this to use spanToJSON(span).description instead as replacement.