Fix noisy "No file system provider found for resource 'gitlab-vscode-ide:/'"

Description

Even on successful runs, the Web IDE starts with this console error:

ERR ENOPRO: No file system provider found for resource 'gitlab-vscode-ide:/'

This occurs because there's some delay between the Web IDE vscode extension being loaded (which initialize

Investigation

Let's try:

• Make sure the gitlab-vscode-ide:/ file system provider is initialized as early as possible in the VSCode extension.
• Initialize the workspace with a temporary file system with scheme of tmp.

Please note:

• Make sure we don't trigger multi-root workspace! For now, we don't want to support this behavior for the Web IDE.