Web updates

HTML 04044721e6f9

Imperatively allocate window agents and agent clusters Previously, the spec vaguely noted that all agents and agent clusters must be allocated at the appropriate time. With this change, similar-origin window agents are allocated imperatively during document and browsing context creation, along with their corresponding agent clusters. The agent clusters are stored in the appropriate browsing context group, via a map keyed by scheme and registrable domain. Fixes #4361. Further work on imperative agent/agent cluster allocation, specifically for workers and worklets, is tracked in #4339.

Dave Tapuska