Editorial: similar-origin window agent

[annevk]

With #4734 a similar-origin window agent might become a single-origin window agent. How do we want to handle this? I suspect we want to keep it as a single type for convenience. Should we change the name?

cc @domenic

[domenic]

I don't think the name is too bad as-is. It's already the case that a "similar-origin window agent" does not contain every realm with a similar origin, because of separation into different BCGs. #4734 just increase the number of cases where similar-origin realms end up in different agents. Stated another way, every realm inside the agent still has a similar origin to each other, so the name is still accurate.

That said, we could just rename it window agent. That's nice and short. The main benefit of the current name is that it makes it really obvious to readers that it isn't a single window, but we have some notes explaining that already, and could add more if we thought it wasn't clear enough.

[annevk]

Even if we keep the name, I should update some of the notes/examples to explain they're conditional on the surrounding agent cluster's cross-origin isolated.