feat(tracing): Upgrade to web-vitals 2.1.0

[AbhiPrasad]

Supercedes #3775

This PR bumps our vendored web-vitals to version 2.1.0. As this bump updated the definition of CLS, we now track the old CLS definition (cls measurement) and the new CLS definition (updated-cls measurement) in the transaction.

We will then cut a beta off this branch and test on Sentry for a couple days. If there isn't a huge discrepancy, we will remove the old CLS definition and move the cls measurement to rely on the updated CLS definition.

Aside from vendoring web-vitals, we also introduced a changelog and noted down the differences between the web-vitals npm package and our vendored version.

TODO:

• Port over web-vitals tests
• Add back old CLS value
• Figure out how to add metadata to alert shift from old CLS -> new CLS definition
• Figure out what changes we can make to vendored in files (since we do leverage BFCache logic)

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	21.46 KB (0%)
@sentry/browser - Webpack	22.47 KB (0%)
@sentry/react - Webpack	22.5 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	28.96 KB (+0.05% 🔺)