[soft-navigation] expose reset for cls and inp on navigation

[mattkubej]

Description

This PR exposes reset functions for the return values of onCLS and onINP. These functions allow for resetting the metric measurements, particularly useful in single-page applications (SPAs) with soft navigation.

Motivation

Surface web-vitals performance signals on soft-navigation within SPAs.

Soft-navigation is an experimental feature within Chrome, but we can instrument SPAs to observe signals during soft-navigation. Resetting the observability of CLS and INP on soft-navigation, as signaled by the client, will provide us additional context on the performance of soft-navigations.

How to use

const { reset: resetCLS } = onCLS(handleCLS, { reportAllChanges: true });
const { reset: resetINP } = onINP(handleINP, { reportAllChanges: true });

function onSoftNavigation() {
 resetCLS();
 resetINP();
}

Similar to the batching example, clients could collect groups of events for each soft-navigation and report on them.

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[tunetheweb]

Hi @mattkubej , thanks for the PR. This has been suggested a few times before, but we are not currently looking to implement this into the library, for the reasons given in #448 (comment) and #448 (comment).

We're hoping to make more progress on the Chrome side this year, and so the soft navs experimental support in this library