Use @google-chrome/web-vitals for CWV measurements

### Description
We currently have a bunch of custom code within `src/performance-impl.js` to calculate CWV values.
There are a couple of compelling reasons I believe it may be worthwhile to switch to using the [web-vitals](https://github.com/GoogleChrome/web-vitals) package.

- Maintenance burden: vitals are going to keep changing. For example the new normalized CLS metric
- Correctness: We've had many bugs in our metric collection. In fact, we still do have a few that Philip Walton found (on top of this latest load/render fiasco)

**caveats**
- We need to measure impact on bundle size
- We have an additional "backgrounding" event that the package doesn't know about which may be relevant for CLS (viewer backgrounding).

### Additional Context

Fixes https://github.com/ampproject/amphtml/issues/33326

Start with src/performance-impl.js and compare the existing CWV measurement flow with the @google-chrome/web-vitals package. Check the bundle-size impact and account for the additional viewer-backgrounding event relevant to CLS. Done means the custom measurement code is replaced without losing that behavior or correctness.

Written by the indexing model from the issue text.