fix(utils): update isClient to check document too

[brc-dd]

Description

The current isClient implementation checks whether window is defined or not. This breaks things when using SSR with Deno as window is defined there (https://deno.land/api@v1.36.1?s=Window)

Additional context

• users can override stuff like this: vuejs/vitepress@e8edd0a, but its not feasible to pass that to every function
• x-ref: remove window variable denoland/deno#13367

---

🤖 Generated by Copilot at 0c222fe

Fixed a bug in isClient function that incorrectly detected browser environments. Changed the function to use document instead of window in packages/shared/utils/is.ts.

🤖 Generated by Copilot at 0c222fe

• Fix bug where isClient returns true in non-browser environments (link)

[brc-dd]

Also, the window parameter of functions doesn't respect undefined and the types don't allow null.

[antfu]

This would be a bit tricky, as document could be later overridden as well. What do you think we check window and document together (does not solve the issue but makes it align more with previous behavior)?

[brc-dd]

Yeah that would work too.