Merge `code-server` and `vscode-web` modules

I think we could merge the two modules, that way we will know for sure that we have feature parity, and it will avoid us from having to update both every time.
It would also make it easier for users to switch if they need to test something.

I suggest we merge both modules into a single `vscode-web` module, and make it possible to select what to use by setting `backend = "code-server" # or vscode-web`.

cc: @matifali