[css-view-transitions-2] Allow passing arbitrary context between Documents for a transition. #8303
Description
The cross-document VT API has a hook for passing opaque contextual data between pages here. The idea being that pages can use this to send information from old to new Document for any customization which is not covered by existing APIs. For example, the location where the user clicked, the current scroll offset on the page etc. It's mean to enable flexibility for use-cases we (API designer) might not be thinking of.
The hook is only relevant for MPA since same-document transitions can already do this trivially with context set up outside of the transition API.