WindowsShellHelper should be available on the extension host as well

[Tyriar]

Currently WindowsShellHelper runs on the renderer process and it is used to classify the current shell on Windows which drives the terminalShellType context key for keybindings as well as the terminal name that shows up in the dropdown. This has always been a debt item that it should be running on the extension host for the remote use case but has never been high priority since it's a small feature that it supports and Windows SSH is fairly new is not a big share of our remote-ssh usage.

This would ideally move to where ever ends up hosting node-pty after the item in #92164 is done.