Support ${localWorkspaceFolder} when cloning in volume

• VSCode Version: Version: 1.63.2 (Universal), Commit: 899d46d82c4c95423fb7e10e68eba52050e30ba3
  -Electron: 13.5.2, Chromium: 91.0.4472.164, Node.js: 14.16.0, V8: 9.1.269.39-electron.0, OS: kernel Darwin x64 21.2.0
• Local OS Version: MacOS 12.1 (21C52) (Monterey)
• Remote OS Version: Debian 11, kernel 5.10.76-linuxkit
• Remote Extension/Connection Type: Docker
• Logs: no relevant logs

Steps to Reproduce:

1. Set up repository for Docker-from-Docker with .devcontainer.
2. Set VS Code to "Clone Repository in Container Volume".
3. Add "remoteEnv": { "LOCAL_WORKSPACE_FOLDER": "${localWorkspaceFolder}" } to devcontainer.json,
4. See that echo $LOCAL_WORKSPACE_FOLDER resolves to a raw string of ${localWorkspaceFolder} inside the container, making it impossible to mount anything in a docker-from-docker scenario.

(This matches #3588, which was closed with this bug unfixed.)

Context: I have a repository with a complex build process involving a number of containers, which I am setting up for Codespaces. Because some prebuilt containers are releases from a private repository/build, I need to run tests on my machine, where they can access the pre-release builds for testing purposes. However, this is not possible, because the configuration that works for Codespaces does not work when run locally. It is probably possible to route around this with a patch hardcoding LOCAL_WORKSPACE_FOLDER, but this being necessary is a bug.