[Chore]: Switch from yarn to a submodule

[jsjoeio]

We currently use yarn link to create a symlink between vendor/modules/code-oss-dev and coder/vscode (our fork). This is a bit unreliable and also requires cloning and updating two separate repos. The first step then would be to switch away from yarn link and use a submodule.

1. Remove vendor
2. Add git submodule under lib/vscode
3. update all the paths and the scripts to point to that location

There may be some additional code to cleanup