ref(tracing): Introduce trace function

[AbhiPrasad]

Figured I would get some code out there as an init starting point. I had another branch with more changes, but abandoned it as it was a bad approach - let's start discussing with this one.

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[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	21.01 KB (-0.01% 🔽)
@sentry/browser - Webpack	21.89 KB (0%)
@sentry/react - Webpack	21.92 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	28.52 KB (+0.43% 🔺)

[AbhiPrasad]

Closing as we are taking a different approach.