Add support for running on web

[mjbvz]

Tracks enabling docs view for the web: GitHub.dev and vscode.dev

[mattbierner]

This branch has the work in progress changes: https://github.com/mattbierner/vscode-docs-view/tree/web-enable

The Shiki update is causing a lot of pain currently. Specifically theme loading kind of is busted. I likely won't be have time to look into this further right now so hoping someone can take the lead on this