Send LCP & CLS as standalone spans

[mydea]

Today, we send INP via a standalone span, to ensure it is captured correctly even if a transaction is not ongoing.

We should do the same for LCP and CLS. (Not sure about others? I guess these are the most relevant ones for this?)

This way, we may also be able to get rid of the "report all changes" code, and we can really only report the final value.

Open questions

• What do we need to change for ingest to make this happen?
• What should the exact span shape be?
• Which web-vitals should be sent standalone - CLS, LCP, INP, what about the others?
• Are there any other blockers to get rid of reportAllChanges?
• This is not backwards compatible, it will require a certain version of self-hosted I guess. Do we care about this?

[cleptric]

Some numbers from SaaS that highlight the potential of collecting more signals.

19.55M page load transactions / 90 days
15.90M FCP measurements / 90days
10.95M CLS measurements / 90 days
10.52M LCP measurements / 90 days