PPR for rerendered dynamic components within non-rerendered layouts

[eric-burel]

Goals

1. Allow a "searchParams()" or "url()" function in RSCs

Background

The blocker for accessing URL in RSCs is that RSC layouts are not rerendered during client-side navigation.
This designs however "leaks" in components, because this also means that no RSC can ever access the URL directly, because they could potentially be within a layout.
This affects RSCs that are never actually rendered in a layout.

The current palliative is using a client-side component and the useSearchParams() hook. Or page-level searchParams props drilling or setting a server-context to pass the value down. There is no component-level pattern that allows accessing searchParams directly in a RSC.

Parallel routes are sometimes mentioned as a palliative but I fail to wrap my head around them for this particular use case.

Slightly related to extending PPR to the layout/page relationship so the layout can define static requirements but pages can be either dynamic or static (currently a static layout won't work with dynamic pages): #44712

Related to this hot issue: #43704

Proposal

All in the title. We could have a mechanism similar to what PPR does for dynamic components within static pages, but for layouts. So a component using search params within a layout would be rerendering during client-side navigation, even if the layout doesn't.