Support VSCode.dev

[mdlmarkham]

I know it's a longshot - but it would be super cool if we could use the Tailscale extension in the VSCode.dev browser environment... this would allow me to connect to my dev sandbox even when I can't install the tailscale client.

[gbraad]

It works on gitpod and with coder's code-server.
vscode.dev for github codespaces should be posible, but not the web-only editor

Node: the fallback could be to use the javascript/wasm SSH client as used in the Tailscale admin menu, if only SSH is a necessity.